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Contributing Authors

MARINA BOUSHRA, MD M. SCOTT MOORE, DO

Resident, Department of Emergency Medicine Research Fellow
East Carolina University/Vidant Medical Center Affiliated Dermatology

THEODORE CRISOSTOMO-WYNNE JUN YEN NG, MD

F. Edward Hébert School of Medicine Intern
Class of 2017 Central Queensland Hospital and Health Services

MATTHEW S. DELFINER SATYAJIT REDDY, MD

New York Institute of Technology College of Osteopathic Medicine Resident, Department of Internal Medicine
Class of 2017 Temple University Hospital

ANGELA GAUTHIER VADIM ROSIN

Yale School of Medicine University of Michigan Medical School
Class of 2018 Class of 2017

BENJAMIN GOUGH, DO SARAH SCHIMANSKY, MB BCh BAO

Resident, Department of General Surgery Academic Foundation Doctor
Christiana Care Health System North Bristol NHS Trust

JAN ANDRE GRAUMAN, MD, MA ZACHARY G. SCHWAM, MD

Family Medicine Resident, Northern Remote Stream Resident, Department of Otolaryngology
University of Manitoba Icahn School of Medicine at Mount Sinai

JESSICA F. JOHNSTON, MSc NINO SIKHARULIDZE, MD

Yale School of Medicine Department of Endocrinology
MD/PhD Candidate Tbilisi State Medical University

JAMES N. McCOY VAISHNAVI VAIDYANATHAN

Texas A&M Health Science Center University of Missouri-Kansas City School of Medicine
Class of 2017 Class of 2018

IMAGE AND ILLUSTRATION TEAM

RYAN W. HADDEN RENATA VELAPATIÑO

University of Alabama School of Medicine San Martín de Porres University
Class of 2017 School of Medicine

vii
Associate Authors
JAMES E. BATES, MD JESSE D. SENGILLO
Resident, Department of Radiation Oncology SUNY Downstate College of Medicine
University of Florida School of Medicine Class of 2018

REED GILBOW, MD WENHUI ZHOU

Resident, Department of Otolaryngology–Head and Neck Surgery Tufts University School of Medicine
University of Virginia School of Medicine MD/PhD Candidate

RYAN KELSCH
Midwestern University Chicago College of Osteopathic Medicine
Class of 2017

IMAGE AND ILLUSTRATION TEAM

NAKEYA KHOZEMA DEWASWALA

Lokmanya Tilak Municipal Medical College
Class of 2016

viii
Faculty Advisors

MARK A.W. ANDREWS, PhD CHARLES S. DELA CRUZ, MD, PhD

Lake Erie College of Osteopathic Medicine at Seton Hill Assistant Professor, Department of Pulmonary and Critical Care Medicine
Greensburg, PA Yale School of Medicine

MARIA ANTONELLI, MD CONRAD FISCHER, MD

Clinical Faculty, Division of Rheumatology Associate Professor, Medicine, Physiology, and Pharmacology
Case Western Reserve University School of Medicine Touro College of Medicine

HERMAN SINGH BAGGA, MD JEFFREY J. GOLD, MD

Urologist, Allegheny Health Network Associate Professor, Department of Neurology
University of Pittsburgh Medical Center Assistant Professor, University of California, San Diego School of Medicine

ADITYA BARDIA, MBBS, MPH RAYUDU GOPALAKRISHNA, PhD

Attending Physician, Massachusetts General Hospital Associate Professor, Department of Cell and Neurobiology
Harvard Medical School Keck School of Medicine of University of Southern California

PAULETTE BERND, PhD RYAN C.W. HALL, MD

Professor, Department of Pathology and Cell Biology Assistant Professor, Department of Psychiatry
Columbia University College of Physicians and Surgeons University of South Florida

SHELDON CAMPBELL, MD, PhD LOUISE HAWLEY, PhD

Associate Professor of Laboratory Medicine Immediate Past Professor and Chair, Department of Microbiology
Yale School of Medicine Ross University School of Medicine

BROOKS D. CASH, MD MARGARET M. HAYES, MD

Professor of Medicine, Division of Gastroenterology Instructor of Medicine
University of South Alabama School of Medicine Harvard Medical School

SHIVANI VERMA CHMURA, MD JEFFREY W. HOFMANN, MD, PhD

Adjunct Clinical Faculty, Department of Psychiatry Resident, Department of Pathology
Stanford University School of Medicine University of California, San Francisco School of Medicine

PETER V. CHIN-HONG, MD BRIAN C. JENSEN, MD

Professor, Department of Medicine Assistant Professor of Medicine and Pharmacology
University of California, San Francisco School of Medicine University of North Carolina Health Care

CHRISTINA E. CIACCIO, MD, MSc CLARK KEBODEAUX, PharmD

Assistant Professor, Departments of Pediatrics and Medicine Clinical Assistant Professor, Pharmacy Practice and Science
The University of Chicago Pritzker School of Medicine University of Kentucky College of Pharmacy

LINDA S. COSTANZO, PhD MICHAEL R. KING, MD

Professor, Physiology & Biophysics Instructor, Department of Pediatric Anesthesiology
Virginia Commonwealth University School of Medicine Northwestern University Feinberg School of Medicine

ANTHONY L. DeFRANCO, PhD KRISTINE KRAFTS, MD

Professor, Department of Microbiology and Immunology Assistant Professor, Department of Basic Sciences
University of California, San Francisco School of Medicine University of Minnesota School of Medicine

ix
GERALD LEE, MD MELANIE SCHORR, MD
Assistant Professor, Department of Pediatrics Research Fellow, Department of Medicine
University of Louisville School of Medicine Massachusetts General Hospital

KACHIU C. LEE, MD, MPH NATHAN W. SKELLEY, MD

Assistant Clinical Professor, Department of Dermatology Assistant Professor, Department of Orthopaedic Surgery
Brown University, Providence, Rhode Island University of Missouri, The Missouri Orthopaedic Institute

WARREN LEVINSON, MD, PhD SHEENA STANARD, MD, MHS

Professor, Department of Microbiology and Immunology Hospitalist
University of California, San Francisco School of Medicine State University of New York Upstate Hospital

PETER MARKS, MD, PhD HOWARD M. STEINMAN, PhD

Center for Biologics Evaluation and Research Assistant Dean, Biomedical Science Education
US Food and Drug Administration Albert Einstein College of Medicine

J. RYAN MARTIN, MD STEPHEN F. THUNG, MD

Assistant Professor of Obstetrics, Gynecology, and Reproductive Sciences Associate Professor, Department of Obstetrics and Gynecology
Yale School of Medicine The Ohio State University College of Medicine

DOUGLAS A. MATA, MD, MPH RICHARD P. USATINE, MD

Brigham and Women’s Hospital Professor, Dermatology and Cutaneous Surgery
Harvard Medical School University of Texas Health Science Center San Antonio

VICKI PARK, PhD PRASHANT VAISHNAVA, MD

Associate Professor, Pediatrics and Medical Education Assistant Professor, Department of Medicine
University of Tennessee Health Science Center Mount Sinai Hospital and Icahn School of Medicine

JEANNINE RAHIMIAN, MD, MBA J. MATTHEW VELKEY, PhD

Associate Professor, Obstetrics and Gynecology Assistant Dean, Basic Science Education
David Geffen School of Medicine at UCLA Duke University School of Medicine

SOROUSH RAIS-BAHRAMI, MD BRIAN WALCOTT, MD

Assistant Professor, Urology and Radiology Clinical Instructor, Department of Neurological Surgery
The University of Alabama at Birmingham School of Medicine University of California, San Francisco

SASAN SAKIANI, MD TISHA WANG, MD

Assistant Professor, Department of Medicine Associate Clinical Professor, Department of Medicine
Case Western Reserve University School of Medicine David Geffen School of Medicine at UCLA

ROBERT A. SASSO, MD SYLVIA WASSERTHEIL-SMOLLER, PhD

Professor of Clinical Medicine Professor Emerita, Department of Epidemiology and Population Health
Ross University School of Medicine Albert Einstein College of Medicine

JOSEPH L. SCHINDLER, MD ADAM WEINSTEIN, MD

Assistant Professor, Neurology and Neurosurgery Assistant Professor, Pediatric Nephrology and Medical Education
Yale School of Medicine Geisel School of Medicine at Dartmouth

x
Preface
With the 27th edition of First Aid for the USMLE Step 1, we continue our commitment to providing students with
the most useful and up-to-date preparation guide for the USMLE Step 1. This edition represents an outstanding
revision in many ways, including:
ƒ 30+ entirely new facts with continued expansion of quality improvement principles, safety science, and healthcare
delivery to align more closely with the USMLE Content Outline.
ƒ Hundreds of major fact updates culled from thousands of student and faculty contributions.
ƒ Extensive text revisions, new mnemonics, clarifications, and corrections curated by a team of more than 25
medical student and resident physician authors who excelled on their Step 1 examinations and verified by a team
of expert faculty advisors and nationally recognized USMLE instructors.
ƒ Complete reorganization of the neurology chapter to better distinguish normal physiology from neuropathology
and to emphasize the special senses.
ƒ Improved Rapid Review section with page numbers to the text, to quickly find these high-yield concepts in
context.
ƒ Updated with more than 100+ new or revised full-color photos to help visualize various disorders, descriptive
findings, and basic science concepts. In particular, imaging photos have been labeled and optimized to show
both normal anatomy and pathologic findings.
ƒ Updated with dozens of new and revised diagrams. We continue to expand our collaboration with USMLE-Rx
(MedIQ Learning, LLC) to develop and enhance illustrations with improved information design to help
students integrate pathophysiology, therapeutics, and diseases into memorable frameworks.
ƒ A revised exam preparation guide with updated data from the USMLE and NRMP. The guide also features new
evidence-based techniques for efficient and effective test preparation. The updated supplemental guide for IMGs,
osteopathic and podiatry students, and students with a disability can be found at our blog, www.firstaidteam.com.
ƒ An updated summary guide to student-recommended USMLE Step 1 review resources, including mobile apps
for iOS and Android. The full resource guide with detailed descriptions can be found at our blog.
ƒ Real-time Step 1 updates and corrections can also be found exclusively on our blog.
We invite students and faculty to share their thoughts and ideas to help us continually improve First Aid for the
USMLE Step 1 through our blog and collaborative editorial platform. (See How to Contribute, p. xvii.)

Louisville Tao Le
Boracay Vikas Bhushan
Philadelphia Matthew Sochat
New York City Yash Chavda
Ann Arbor Andrew Zureick
Pittsburgh Mehboob Kalani
San Francisco Kimberly Kallianos

xi
Special Acknowledgments
This has been a collaborative project from the start. We gratefully acknowledge the thousands of thoughtful
comments, corrections, and advice of the many medical students, international medical graduates, and faculty who
have supported the authors in our continuing development of First Aid for the USMLE Step 1.
We provide special acknowledgment and thanks to the following individuals who made exemplary contributions to this
edition through our voting, proofreading, and crowdsourcing platform: Anosh Ahmed, Kashif Badar, Humood Boqambar,
Anup Chalise, Wendy Chen, Francis Deng, Anthony J. Febres, Okubit Gebreyonas, Richard Godby, Christina Govas, Eric
Irons, Nikhar Kinger, Katherine Kramme, Jonathan Li, Micah Mathai, Nicolaus Mephis, Ryan Meyer, Joseph Mininni,
Iraj Nasrabadi, Jimmy Tam Huy Pham, Keyhan Piranviseh, Anthony Purgianto, Casey Joseph Rosenthal, Sana Sheraz,
Avinainder Singh, Paul Walden, Isabella Wu, and Xuebao Zhang. For illustration contributions, we also thank Wendy
Abbott.
For support and encouragement throughout the process, we are grateful to Thao Pham, Jinky Flang, and Jonathan
Kirsch, Esq. Thanks to Louise Petersen for organizing and supporting the project. Thanks to our publisher, McGraw-
Hill, for the valuable assistance of its staff, including Christina Thomas, Jim Shanahan, Laura Libretti, Midge
Haramis, and Jeffrey Herzich.
We are also very grateful to Dr. Fred Howell and Dr. Robert Cannon of Textensor Ltd for providing us extensive
customization and support for their powerful Annotate.co collaborative editing platform (www.annotate.co), which
allows us to efficiently manage thousands of contributions. Thanks to Dr. Richard Usatine for his outstanding
dermatologic and clinical image contributions. Thanks also to Jean-Christophe Fournet (www.humpath.com), Dr.
Ed Uthman, and Dr. Frank Gaillard (www.radiopaedia.org) for generously allowing us to access some of their striking
photographs. We especially thank Dr. Kristine Krafts for many insightful text and image contributions throughout the
extensive revision.
For exceptional editorial leadership, enormous thanks to Christine Diedrich, Emma Underdown, and Catherine
Johnson. Thank you to our USMLE-Rx/ScholarRx team of editors, Linda Davoli, Jacqueline Mahon, Janene
Matragrano, Erika Nein, Isabel Nogueira, Rebecca Stigall, Ashley Vaughn, and Hannah Warnshuis. Many thanks to
Tara Price for page design and all-around InDesign expertise. Special thanks to our indexer Dr. Anne Fifer. We are
also grateful to our medical illustrator, Hans Neuhart, for his creative work on the new and updated illustrations. Lastly,
tremendous thanks to Rainbow Graphics, especially David Hommel and Donna Campbell, for remarkable ongoing
editorial and production support under time pressure.

Louisville Tao Le
Boracay Vikas Bhushan
Philadelphia Matthew Sochat
New York City Yash Chavda
Ann Arbor Andrew Zureick
Pittsburgh Mehboob Kalani
San Francisco Kimberly Kallianos

xii
General Acknowledgments

Each year we are fortunate to receive the input of thousands of medical students and graduates who provide new material, clarifications,
and potential corrections through our website and our collaborative editing platform. This has been a tremendous help in clarifying
difficult concepts, correcting errata from the previous edition, and minimizing new errata during the revision of the current edition. This
reflects our long-standing vision of a true, student-to-student publication. We have done our best to thank each person individually
below, but we recognize that errors and omissions are likely. Therefore, we will post an updated list of acknowledgments at our website,
www.firstaidteam.com/bonus/. We will gladly make corrections if they are brought to our attention.

For submitting contributions and corrections, many thanks to Mohammed Abed, Asif Abidi, John David Adame, Poppy Addison, Onaola
Adedeji, Comfort Agaba, Vivian Agumadu, Bilawal Ahmed, Zoey Akah, Hamed Akbari, Pegah Akbari, Marwan Alahiri, Fadi Al-Asadi,
Lourdes Alberty, Christian Alch, Erica Alcibiade, Majed Alghamdi, Mohammed Alhaidar, Nasir Alhamdan, Albert Alhatem, Alaa
Alibrahim, Mohammed Alsaggaf, Luai M. Alsakaf, Khaled Al-Sawalmeh, Vaidehi Ambai, Kevin An, Anna Anderson, Christopher
Anderson, Mehdi Ansari, Nelson Arellano, Gabriel Arom, Immad Attique, Nicholas Austin, Mary Ayad, Cho New Aye, Marwan Azzam,
Ram Baboo, Rahaf Baker, Brian Baksa, Vijay Balakrishnan, Vyshnavy Balendra, Melissa Banez, Gauri Barlingay, Ross Barman, Frances M.
Marrero Barrera, Josh Barrick, Jason Batey, Priya Batta, Rosemary Noel Beavers, Sean Behan, Jorge Martinez Bencosme, Kene Ben-
Okafor, Elodie Marie Betances, Maria Betances, Shea Bielby, Johnathon Bishop, Aaron Blackshaw, Edgar Blecker, Cary Blum, Peter
Boateng, Nwamaka Bob-Ume, Victoria Bone, Stephanie Borinsky, Adam Bortner, Chantal Brand, Shannon Brougher, Sareena Brown,
Rob Brumer, Ryan Brunetti, Takur Buck, Alejandro Bugarini, Nimerta Burmhi, James Butz, Jennifer Byrd, Stefan Campbell, Fiorella B.
Castillo, Harold Cedeño, Kenan Celtik, Yusuf Chao, Kyriakos Chatzopoulos, Jessica Chen, Julia Chen, Stephanie Yi-Tsi Chen, Willie Chen,
Charlie Cheng, Olivia Cheng, Shani Chibber, Tiffany Chomko, Manita Choudhary, Eric Christie, Melissa Chung, Casey Lane Clark, Beth
Clymer, Sam Cochran, Lauren Coleman, Benjamin Comora, Jensyn Cone, Zachary R. Conley, Sarah Corral, Eliana Costantino, Ian Cox,
Robert Cox, Crosby Culp, John Cummins, Helen Dainton, Christopher Dallo, Jonathan Dang, Laura Dankovich, Atman Dave, Eric Davied,
Joshua Davis, Danielle Davis, Solomon Dawson, Ezra Dayan, Ryan DeAngelis, Kathryn Demitruk, Jessie Dhaliwal, Rahim Dhanani, Travis
Dice, Abiot Didana, Cheri Dijamco, Ozan Dikilitas, Isaac M. Dodd, Kirsten Dowling, Mitch Dunklebarger, Khanh Duong, Marco Duverseau,
Josh East, Jeremy Eckes, Elise Edoka, Rachel Einarsson, Hannah Eisen, Tyler Emerson, Jon Erdman, Cynthia Estrada, Matthew Fadus,
Giselle Falconi, Tabbassum Fayyaz, Ravali Feeramachaneni, Kaveh Fekri, Albert Fernandez, Maria Vanessa Ferrer, Roberto Hurtado Fiel,
Nicholas Field, Ryan Finn, Helen Francis, Daniel Franco, Cameron Frederick, Eli Fredman, Sheri Frickey, Gianfranco Frojo, Malak Fuad,
James Fuqua, Anita Gade, Sudha Gade, Nicholas Gamboa, Avi Gandi, Jared Gans, Russell Garcia, P. M. Gayed, Nicholas Geiger, Alejandro
Gener, John George, Maikel Ragaei Fahmi Gerges, Imran Ghare, Gaby Ghobrial, Javid Ghomashi, Gino Giannone, Lizz Gilmore, Priscilla
Alvarez Gonzalez, Luis Fernando Gonzalez-Ciccarelli, Ashwani Gore, Sophie Gott, Crystal D. Green, Brian Grice, John Grotberg, Li Guiqin,

xiii
Nita Gupta, Gail Gutman, Samuel Guyer, Natalia Guzmman-Seda, Fuad Habbal, Sean M. Hacking, Erik Haley, Oday Halhouli, Martin
Halicek, Isaiah Hammonds, Nicola Hampel, Brian Handal, Roy Handelsman, Jamison Harvey, Hunaid Hasan, Makenzie Hatfield Kresch,
Joel Hayden, Mona Hdeib, Kasey Helmlinger, Katy Helms, Michelle Herberts, Cinthia Marie Gonzalez Hernandez, Ariana Hess, Mitchell
Heuermann, Richard Hickman, Tiffany Hinojosa, Joyce Ho, M. Ho, Patrick Holman, Jeffeory Howard, Paige Hoyer, Jonathan C. Hu, Ann
Hua, Jack Hua, I-Chun Hung, Frank S. Hurd, Ibrahim Hyder, David Ianacone, Jouzif Ibrahim, Taylin Im, Saira Iqbal, Josh Isserman,
Mimoza Isufi, Kelechi Izunobi, Pegah Jahangiri, Sakshi Jain, Maryam Mohammed Jallo, Mitra Jamshidian, Neetu Jamwal, Paige Jarmuz,
Zahran Jdaitawi, Kyu-Jin Jeon, Benjamin Hans Jeuk, Jose F. Jimenez, Sally Jo, Alfredo Joffre, Andrew Johnson, Jordan E. Johnson, Kai
Johnson, Katherine Joltikov, Gavin Jones, Saman Doroodgar Jorshery, Vaidehi Joshi, Shirley Ju, Michael Kagan, Hanna Kakish, Kirill
Karlin, Michael Karp, Aaron R. Kaufman, LaDonna Kearse, Sorena Keihani, Shamim Khan, Tamer Khashab, Mitra Khosravi, Amin
Khosrowpour, Neharika Khurana, Beom Soo Kim, Christina Kim, Robert Kim, Yoo Jung Kim, Megan King, Vladimer Kitiashvili, David E.
Klein, Mohammed Sammy Knefati, George Koch, Noah Kojima, Amol Koldhekar, Samantha Kops, Sai Krishna Korada, Zachary Koretz,
Heather Kornmehl, David Kowal, Kathleen Kramer, Akash Kroeger, Elan Krojanker, Matthew Kurian, Anita Kurre, Rachel Kushner,
Eustina Kwon, Michael Larson, George Lasker, Evangelia Lazaris, Aaron A. Lebron Burgos, Christina Dami Lee, James Lee, Jennifer Lee,
Erica Lee, Rachel Leeman, Ryan Lena, Stacy Leung, Guanqun Li, Yedda Li, Ramon Li, Guohua Liang, Soobin Lim, Meng-Chen Vanessa
Lin, Matthew Lippmann, Selina Liu, Alnardo Lora, Yancheng Luo, Ahmed Lutfi, Martin Ma, Ahmad Mahadeen, Nandita N. Mahajan,
Gajendra Maharjan, Megan Maier, Nodari Maisuradze, Rohail Malik, Andrew Martella, Beatriz Martinez, Eden Marx, Christy Mathew,
Aletha Anisha Mathias, Alex McDonald, Robert McKenna, Maggie Meier, Wendy Mejia, Theresa Meloche, Elizabeth Mertilus, Jersey
Mettille-Butts, Marielle Meurice, Sarah Michelson, Austin Mike-Mayer, Nardine Mikhail, Vincent Mirabile, Ahmed Mohamed, Hassan
Reyad Mohsen, Nate Moore, Rose Mueller, Amer Muhyieddeen, Natia Murvelashvili, Anadarajan Nadarajan, Louai Naddaf, Shane
Naidoo, Khushabu Nayak, Mai-Trang Nguyen, Michael Nguyen, Thomas Nienaber, Bharati Nimje, Cynthia Noguera, Albert Nwabueze,
Devon O’Brien, Lola Ogunsuyi, Ololade Ogunsuyi, Olguta Olea, Wilson Omesiete, Michael Osinski, Vasily Ovechko, Jordan Owens, Devon
Pace, Zonghao Pan, Khang Wen Pang, Olga Paniagua, Silvia Paola, Erika Parisi, Andrew Park, Madhumithaa Parthasarathy, Ishan Patel,
Saikrishna Patibandla, Iqra Patoli, David Patterson, Lanieka Peck, Alexander Pennekamp, Luisa Peress, Max Petersen, Romela
Petrosyan, Patryk Piekos, Sarah Pietruszka, Luis Pina, Yuval Pinto, Andrew Piropato, Phillip Plager, Netanya Pollock, Gautham
Prabhakar, Will Preston, Grace Pryor, Audrey Pulitzer, Tyler Putnam, Connie Qiu, Brian Quaranto, Fatima Quddusi, Carlos Quinonez,
Maria Qureshi, Samir Rahman, Saad Rahmat, Alia Raja, Vinaya Rajan, Arun Rajaratnam, Ferza Raks, Juhi Ramchandani, Judith Ramel,
Josean Ramos, Cesar Augusto Hernandez Rangel, Dhakshitha Rao, Mohsin Raza, Sushma Reddy, Dave Reyes, Lenisse Miguelina Reyes,
Robert Riggio, Ernest James Rin, Julia Ringel, Moshe Roberts, Clara Robertson, Sam Robinson, Agalic Rodriguez, Juliana D. Rodriguez,
Jorge Roman, Luis Rosario, Alexander Rowan, Julietta Rubin, Daniel Rubinger, Martin Runnström, Nicholas Russo, David Rutenberg,
Sean Saadat, Stuart Sacks, Rorita Sadhu, Atin Saha, Haneen Salah, Mohamad Saleh, Rafael E. Valle Salinas, Jacqueline Sanchez, Natalia
Santiago-Morales, Steven Sapozhnikov, Ashley Sareen, Jason Sarte, Claire Sathe, Darya Savel, Osama Sbeitan, Ghil Schwarz, Caleb
Seavey, Roopak Sekhon, Anna Sevilla, Anand Sewak, Akash Shah, Anna Shah, Muneeb Shah, Sherina Shahbazian, Abdulla Shaheen,
Ojochide Shaibu, Mhd Tayseer Shamaa, Bryan Shapiro, Dolly Sharma, Demetrio Sharp, Jia Shi, Helen Shi, Ryan Sieli, Tyler Simpson, Vikal
Singh, Chandandeep Singh, Ramzi Skaik, Omar Abu Slieh, Joey Sneij, Navjot Sobti, Tom Soker, Jun Song, Sushant Soni, Mihir Soparkar,
Vlasios Sotirchos, Amelia St.Ange, Mac Staben, Clay Stafford, Allan Stolarski, Sonia A Sugumar, Mark Anthony Sy, Angela Taeschner,
Dawood Tafti, Nitin Tandan, David Taylor, Abiolah Telesford, George Terre, Sam Thomas, Akhilesh Thota, Sandra Tomlinson-Hansen,
Carlos E. Velez Torres, Derrick Tran, Vi Tran, Michael Troutman, Cindy L. Tsui, Harika R. Tula, Michael Turgeon, Esonoes Tururu, Marcia
Uddoh, Daniel Udrea, Nkechi Ukeekwe, Sara Usman, Akash Vadhavana, Royson L. Vallliyil, Leah D. Vance, Blanca Vargas, Alexander

xiv
Vartanov, Jayalakshmi Venkateswaran, Bhanu Verma, Shawn Verma, Andrea Victorio, Anthony Viola III, Miriam Volosen, Habiba Wada,
Benjamin Warren, Juliana Watson, Hannah Wellman, Stanley J. Welsh, Pang Khang Wen, Richard Whitlock, Jimbo Wilhite, Michael
Winter, Jonathan Wolfson, John Worth, Eva Wu, Birdy Xu, Antonio Yaghy, Jehan Yahya, Xiaofeng Yan, Rebecca Ye, Raquel Yokoda,
Alexander Yuen, William Yuen, Alan Zats, Billy Zhang, Park Zheng, and Andrew Zilavy.

xv
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How to Contribute

This version of First Aid for the USMLE Step 1 incorporates thousands of contributions and improvements suggested
by student and faculty advisors. We invite you to participate in this process. Please send us your suggestions for:

ƒ Study and test-taking strategies for the USMLE Step 1

ƒ New facts, mnemonics, diagrams, and clinical images

ƒ High-yield topics that may appear on future Step 1 exams

ƒ Personal ratings and comments on review books, question banks, apps, videos, and courses

For each new entry incorporated into the next edition, you will receive up to a $20 Amazon.com gift card as well as
personal acknowledgment in the next edition. Significant contributions will be compensated at the discretion of the
authors. Also, let us know about material in this edition that you feel is low yield and should be deleted.

All submissions including potential errata should ideally be supported with hyperlinks to a dynamically updated Web
resource such as UpToDate, AccessMedicine, and ClinicalKey.

We welcome potential errata on grammar and style if the change improves readability. Please note that First Aid style
is somewhat unique; for example, we have fully adopted the AMA Manual of Style recommendations on eponyms
(“We recommend that the possessive form be omitted in eponymous terms”) and on abbreviations (no periods with
eg, ie, etc).

The preferred way to submit new entries, clarifications, mnemonics, or potential corrections with a valid,
authoritative reference is via our website: www.firstaidteam.com.

This website will be continuously updated with validated errata, new high-yield content, and a new online platform
to contribute suggestions, mnemonics, diagrams, clinical images, and potential errata.

Alternatively, you can email us at: firstaidteam@yahoo.com.

Contributions submitted by May 15, 2017, receive priority consideration for the 2018 edition of First Aid for the
USMLE Step 1. We thank you for taking the time to share your experience and apologize in advance that we cannot
individually respond to all contributors as we receive thousands of contributions each year.

xvii
 `
NOTE TO CONTRIBUTORS

All contributions become property of the authors and are subject to editing and reviewing. Please verify all data and
spellings carefully. Contributions should be supported by at least two high-quality references.

Check our website first to avoid duplicate submissions. In the event that similar or duplicate entries are received,
only the first complete entry received with valid, authoritative references will be credited. Please follow the style,
punctuation, and format of this edition as much as possible.

`
JOIN THE FIRST AID TEAM

The First Aid author team is pleased to offer part-time and full-time paid internships in medical education and
publishing to motivated medical students and physicians. Internships range from a few months (eg, a summer) up
to a full year. Participants will have an opportunity to author, edit, and earn academic credit on a wide variety of
projects, including the popular First Aid series.

For 2017, we are actively seeking passionate medical students and graduates with a specific interest in improving our
medical illustrations, expanding our database of medical photographs, and developing the software that supports our
crowdsourcing platform. We welcome people with prior experience and talent in these areas. Relevant skills include
clinical imaging, digital photography, digital asset management, information design, medical illustration, graphic
design, and software development.

Please email us at firstaidteam@yahoo.com with a CV and summary of your interest or sample work.

xviii
How to Use This Book
CONGRATULATIONS: You now possess the book that has guided nearly two million students to USMLE success
for over 25 years. With appropriate care, the binding should last the useful life of the book. Keep in mind that putting
excessive flattening pressure on any binding will accelerate its failure. If you purchased a book that you believe
is defective, please immediately return it to the place of purchase. If you encounter ongoing issues, you can also
contact Customer Service at our publisher, McGraw-Hill Education, at https://www.mheducation.com/contact.html.

START EARLY: Use this book as early as possible while learning the basic medical sciences. The first semester of
your first year is not too early! Devise a study plan by reading Section I: Guide to Efficient Exam Preparation, and
make an early decision on resources to use by checking Section IV: Top-Rated Review Resources. Note that First Aid
is neither a textbook nor a comprehensive review book, and it is not a panacea for inadequate preparation.

CONSIDER FIRST AID YOUR ANNOTATION HUB: Annotate material from other resources, such as class
notes or comprehensive textbooks, into your book. This will keep all the high-yield information you need in one
place. Other tips on keeping yourself organized:

ƒ For best results, use fine-tipped ballpoint pens (eg, BIC Pro+, Uni-Ball Jetstream Sports, Pilot Drawing Pen,
Zebra F-301). If you like gel pens, try Pentel Slicci, and for markers that dry almost immediately, consider
Staedtler Triplus Fineliner, Pilot Drawing Pen, and Sharpies.

ƒ Consider using pens with different colors of ink to indicate different sources of information (eg, blue for
USMLE-Rx Step 1 Qmax, green for UWorld Step 1 Qbank).

ƒ Choose highlighters that are bright and dry quickly to minimize smudging and bleeding through the page
(eg, Tombow Kei Coat, Sharpie Gel).

ƒ Many students de-spine their book and get it 3-hole-punched. This will allow you to insert materials from other
sources, such as course syllabi.

INTEGRATE STUDY WITH CASES, FLASH CARDS, AND QUESTIONS: To broaden your learning strategy,
consider integrating your First Aid study with case-based reviews (eg, First Aid Cases for the USMLE Step 1), flash
cards (eg, First Aid Flash Facts), and practice questions (eg, the USMLE-Rx Step 1 Qmax). Read the chapter in the
book, then test your comprehension by using cases, flash cards, and questions that cover the same topics. Maintain
access to more comprehensive resources (eg, First Aid for the Basic Sciences: General Principles and Organ Systems
and First Aid Express videos) for deeper review as needed.

PRIME YOUR MEMORY: Return to your annotated Sections II and III several days before taking the USMLE
Step 1. The book can serve as a useful way of retaining key associations and keeping high-yield facts fresh in your
memory just prior to the exam. The Rapid Review section includes high-yield topics to help guide your studying.

CONTRIBUTE TO FIRST AID: Reviewing the book immediately after your exam can help us improve the next
edition. Decide what was truly high and low yield and send us your comments. Feel free to send us scanned images
from your annotated First Aid book as additional support. Of course, always remember that all examinees are under
agreement with the NBME to not disclose the specific details of copyrighted test material.

xix
Selected USMLE Laboratory Values

* = Included in the Biochemical Profile (SMA-12)

Blood, Plasma, Serum Reference Range SI Reference Intervals

*Alanine aminotransferase (ALT, GPT at 30°C) 8–20 U/L 8 –20 U/L

Amylase, serum 25–125 U/L 25–125 U/L
*Aspartate aminotransferase (AST, GOT at 30°C) 8–20 U/L 8–20 U/L
Bilirubin, serum (adult)
Total // Direct 0.1–1.0 mg/dL // 0.0–0.3 mg/dL 2–17 μmol/L // 0–5 μmol/L
*Calcium, serum (Total) 8.4–10.2 mg/dL 2.1–2.8 mmol/L
*Cholesterol, serum (Total) < 200 mg/dL < 5.2 mmol/L
*Creatinine, serum (Total) 0.6–1.2 mg/dL 53–106 μmol/L
Electrolytes, serum
Sodium 136–145 mEq/L 136–145 mmol/L
Chloride 95–105 mEq/L 95–105 mmol/L
* Potassium 3.5–5.0 mEq/L 3.5–5.0 mmol/L
Bicarbonate 22–28 mEq/L 22–28 mmol/L
Magnesium 1.5 mEq/L 0.75–1.0 mmol/L
Gases, arterial blood (room air)
PO 2 75–105 mm Hg 10.0–14.0 kPa
PCO2 33–44 mm Hg 4.4–5.9 kPa
pH 7.35–7.45 [H+] 36–44 nmol/L
*Glucose, serum Fasting: 70–110 mg/dL 3.8–6.1 mmol/L
2-h postprandial: < 120 mg/dL < 6.6 mmol/L
Growth hormone − arginine stimulation Fasting: < 5 ng/mL < 5 μg/L
provocative stimuli: > 7 ng/mL > 7 μg/L
Osmolality, serum 275–295 mOsm/kg 275–295 mOsm/kg
*Phosphatase (alkaline), serum (p-NPP at 30°C) 20–70 U/L 20–70 U/L
*Phosphorus (inorganic), serum 3.0–4.5 mg/dL 1.0–1.5 mmol/L
Prolactin, serum (hPRL) < 20 ng/mL < 20 μg/L
*Proteins, serum
Total (recumbent) 6.0–7.8 g/dL 60–78 g/L
Albumin 3.5–5.5 g/dL 35–55 g/L
Globulins 2.3–3.5 g/dL 23–35 g/L
*Urea nitrogen, serum (BUN) 7–18 mg/dL 1.2–3.0 mmol/L
*Uric acid, serum 3.0–8.2 mg/dL 0.18–0.48 mmol/L
(continues)

xx
Cerebrospinal Fluid Reference Range SI Reference Intervals

Glucose 40–70 mg/dL 2.2–3.9 mmol/L

Hematologic

Erythrocyte count Male: 4.3–5.9 million/mm3 4.3–5.9 × 1012/L

Female: 3.5–5.5 million/mm3 3.5–5.5 × 1012/L
Erythrocyte sedimentation rate (Westergen) Male: 0–15 mm/h 0–15 mm/h
Female: 0–20 mm/h 0–20 mm/h
Hematocrit Male: 41–53% 0.41–0.53
Female: 36–46% 0.36–0.46
Hemoglobin, blood Male: 13.5–17.5 g/dL 2.09–2.71 mmol/L
Female: 12.0–16.0 g/dL 1.86–2.48 mmol/L
Hemoglobin, plasma 1–4 mg/dL 0.16–0.62 μmol/L
Leukocyte count and differential
Leukocyte count 4500–11,000/mm3 4.5–11.0 × 109/L
Segmented neutrophils 54–62% 0.54–0.62
Band forms 3–5% 0.03–0.05
Eosinophils 1–3% 0.01–0.03
Basophils 0–0.75% 0–0.0075
Lymphocytes 25–33% 0.25–0.33
Monocytes 3–7% 0.03–0.07
Mean corpuscular hemoglobin 25.4–34.6 pg/cell 0.39–0.54 fmol/cell
Mean corpuscular volume 80–100 μm3 80–100 fL
Partial thromboplastin time (activated) 25–40 seconds 25–40 seconds
Platelet count 150,000–400,000/mm3 150–400 × 109/L
Prothrombin time 11–15 seconds 11–15 seconds
Reticulocyte count 0.5–1.5% of red cells 0.005–0.015
Sweat

Chloride 0–35 mmol/L 0–35 mmol/L

Urine

Proteins, total < 150 mg/24 h < 0.15 g/24 h

xxi
 First Aid Checklist for the USMLE Step 1

This is an example of how you might use the information in Section I to prepare for the USMLE Step 1. Refer
to corresponding topics in Section I for more details.

Years Prior
□ Select top-rated review resources as study guides for first-year medical school courses.
□ Ask for advice from those who have recently taken the USMLE Step 1.

Months Prior
□ Review computer test format and registration information.
□ Register six months in advance. Carefully verify name and address printed on scheduling permit. Call
Prometric or go online for test date ASAP.
□ Define goals for the USMLE Step 1 (eg, comfortably pass, beat the mean, ace the test).
□ Set up a realistic timeline for study. Cover less crammable subjects first. Review subject-by-subject
emphasis and clinical vignette format.
□ Simulate the USMLE Step 1 to pinpoint strengths and weaknesses in knowledge and test-taking skills.
□ Evaluate and choose study methods and materials (eg, review books, question banks).

Weeks Prior
□ Simulate the USMLE Step 1 again. Assess how close you are to your goal.
□ Pinpoint remaining weaknesses. Stay healthy (exercise, sleep).
□ Verify information on admission ticket (eg, location, date).

One Week Prior

□ Remember comfort measures (loose clothing, earplugs, etc).
□ Work out test site logistics such as location, transportation, parking, and lunch.
□ Call Prometric and confirm your exam appointment.

One Day Prior

□ Relax.
□ Lightly review short-term material if necessary. Skim high-yield facts.
□ Get a good night’s sleep.
□ Make sure the name printed on your photo ID appears EXACTLY the same as the name printed on your
scheduling permit.

Day of Exam
□ Relax. Eat breakfast. Minimize bathroom breaks during the exam by avoiding excessive morning caffeine.
□ Analyze and make adjustments in test-taking technique. You are allowed to review notes/study material
during breaks on exam day.

After the Exam

□ Celebrate, regardless.
□ Send feedback to us on our website at www.firstaidteam.com.

xxii
SECTION I

Guide to Efficient
Exam Preparation

“A mind of moderate capacity which closely pursues one study must ` Introduction 2
infallibly arrive at great proficiency in that study.”
—Mary Shelley, Frankenstein ` USMLE Step 1—The
Basics 2
“Finally, from so little sleeping and so much reading, his brain dried up
and he went completely out of his mind.” ` Defining Your Goal 12
—Miguel de Cervantes Saavedra, Don Quixote
` Excelling in the
“Sometimes the questions are complicated and the answers are simple.” Preclinical Years 13
—Dr. Seuss
` Timeline for Study 14
“He who knows all the answers has not been asked all the questions.”
—Confucius ` Study Materials 18
“It’s what you learn after you know it all that counts.”
` Test-Taking
—John Wooden
Strategies 20
“A goal without a plan is just a wish.”
` Clinical Vignette
—Antoine de Saint-Exupéry
Strategies 21

` If You Think You

Failed 22

` Testing Agencies 22

` References 23

1
2 SEC TION I GUIDE TO EFFICIENT EXAM PREPARATION

`
INTRODUCTION

Relax.

This section is intended to make your exam preparation easier, not harder.
Our goal is to reduce your level of anxiety and help you make the most of
your efforts by helping you understand more about the United States Medical
Licensing Examination, Step 1 (USMLE Step 1). As a medical student, you
are no doubt familiar with taking standardized examinations and quickly
absorbing large amounts of material. When you first confront the USMLE
Step 1, however, you may find it all too easy to become sidetracked from your
goal of studying with maximal effectiveness. Common mistakes that students
make when studying for Step 1 include the following:

ƒ Starting to study (including First Aid) too late

ƒ Starting to study intensely too early and burning out
ƒ Starting to prepare for boards before creating a knowledge foundation
ƒ Using inefficient or inappropriate study methods
ƒ Buying the wrong resources or buying too many resources
ƒ Buying only one publisher’s review series for all subjects
ƒ Not using practice examinations to maximum benefit
ƒ Not understanding how scoring is performed or what the score means
` The test at a glance: ƒ Not using review books along with your classes
ƒ 8-hour exam ƒ Not analyzing and improving your test-taking strategies
ƒ Total of 280 multiple choice items ƒ Getting bogged down by reviewing difficult topics excessively
ƒ 7 test blocks (60 min/block) ƒ Studying material that is rarely tested on the USMLE Step 1
ƒ Up to 40 test items per block ƒ Failing to master certain high-yield subjects owing to overconfidence
ƒ 45 minutes of break time, plus another 15 ƒ Using First Aid as your sole study resource
if you skip the tutorial ƒ Trying to prepare for it all alone

In this section, we offer advice to help you avoid these pitfalls and be more
productive in your studies.

`
USMLE STEP 1—THE BASICS

The USMLE Step 1 is the first of three examinations that you must pass in
order to become a licensed physician in the United States. The USMLE is
a joint endeavor of the National Board of Medical Examiners (NBME) and
the Federation of State Medical Boards (FSMB). The USMLE serves as the
single examination system for US medical students and international medical
graduates (IMGs) seeking medical licensure in the United States.
Another random document with
no related content on Scribd:
sweet and lovely in English womanhood would soon be his to have and to
hold for ever.

Her eyes, large, brown, and true, were fixed steadfastly on him, and
found no less pleasure in what they saw than his did. In his evening dress
Ralph looked taller than the six feet that he actually measured; fair hair
curled crisply over a sun-tanned face, in every line of which frank candour
was written, and his athletic figure was graceful in every involuntary pose.
Gwendolen had reason to be proud of her lover as he thus stood silhouetted
against the moonlit sky, and she made no secret of it to herself that she
found pleasure in his unconscious show of great strength in restraint. He
could kill her with so little effort of those well-shaped, nervous hands, and
yet one look from her could make his whole frame tremble.

So in silence they communed together, as is the way with lovers who

know that no words can express a tithe of their deep emotion. And, indeed,
while lovers have eyes to see, they do not need tongues to speak. Silence is
best when two hearts are in accord.

The silence was broken by Sir Geoffrey's voice talking to Mrs. Austen
as they came over the velvety turf. Sir Geoffrey helped his companion on to
the houseboat and followed her up the stairway.

"Forgive us for being so long, Gwendolen," he said in his cheery,

bantering fashion. "I hope my nephew has been doing his best to entertain
you."

"He has been behaving very nicely," Gwendolen replied, "and I think
you have brought him up very well."

"I told Martin to bring us some coffee and liqueurs," Sir Geoffrey went
on, "and I'm going to smoke, if you ladies will allow me, and look at the
reflections in the water, and fancy I'm young again."

Mrs. Austen protested.

"You are young, until you feel old," she said, "and you don't feel that to-
night."
 "No, I don't," said Sir Geoffrey stoutly. "This is an ideal ending to one
of the happiest days of my life, and if a man is only as old as he feels, I
shall come of age on Ralph's wedding-day." He lighted a cigar and flung the
match into the river. "Have a cigar, Ralph? I'm sure you have earned it."
The old fellow was pleased that his nephew could not chime in with his
trivial chatter, and pulling up a chair by Gwendolen's side, he patted her
hand. "Happy, Gwen?" he asked, and as the answering smile dawned in the
girl's dark eyes, he wiped his own, which suddenly grew misty. "That's
right, that's right," he said quickly. "Ah! here is Martin with the tray."

Allured by the material pleasures of tobacco and liqueurs, Ralph

descended to earth again, and soon the little party were laughing and
chatting merrily enough. Soft strains of music from another houseboat were
carried down to them, and presently a young fellow poled a racing punt
swiftly down the stream; two swans floated out from underneath the trees,
rocking gracefully on the water ruffled by the punt; and from the tender
came suggestively domestic sounds as the old butler put away the cups and
saucers and decanted whiskey for the men.

Then presently they strolled back to the manor house and lingered for a
little in the hall; and while Ralph took his time to bid Gwendolen good-
night, Sir Geoffrey found opportunity to say a few more words to Mrs.
Austen.

"I wish I could tell you how happy I am," he said. "I have hoped for this
all my life, and now it has come to pass. They both are worthy of each
other, and to see such happiness as theirs is almost as good as having it
oneself."

Mrs. Austen cordially agreed, but she wondered if Sir Geoffrey's hearty
words were at all belied by the sigh that accompanied them. Yet she stifled
the suspicion as it was born, for no woman lives long enough to give her
child in marriage without learning the truth that underlies the words:

"Our sincerest laughter

With some pain is fraught;
Our sweetest songs are those that
tell of saddest thought."
Then, with the curiosity of her sex, she wondered again, as she had so often
wondered before, why Sir Geoffrey Holt himself had never married.

CHAPTER III.

FRAUD.

Rather more than a week elapsed, during which Melville saw practically
nothing of the outer world. His chambers were at the top of the house in
Jermyn Street, the suite consisting of a sitting, bed, and bath rooms, which
he rented furnished for seventy pounds a year. His food and attendance
were all supplied to him by the general manager of the house, and his credit
for these bare necessaries of life was still good. So Melville gave orders to
the hall porter to reply uniformly to all enquirers that he was not at home,
and remained in his chambers steeped in dull melancholy. One evening he
stole out and pawned his violin, but that very night he lost nearly all the
proceeds of the transaction in some utterly foolish wager, and the next
morning he woke up face to face with the fact that he only possessed ten
shillings in the world. It was pouring with rain and the wind was howling
round the balustrade outside his windows. Melville shivered; he felt cold
and ill, and recollected that he had eaten no dinner the night before. He rang
the bell and told the valet, whose services he shared with the other tenants
on his floor, to bring him up some breakfast and some shaving water.

"What is the time?" he asked curtly, as the man came from his bedroom
to say the shaving water was ready.

"About twelve, sir. I will bring up your breakfast in a quarter of an

hour."

Melville turned to the window again. If only the rain would stop! And
how he missed his violin! No human being could realise what his
instrument had been to him, or what a wrench it had been to part with it. He
felt utterly destitute.

"What am I to do?" he muttered vainly. "Sir Geoffrey—no, it's worse

than useless to apply to him—last time was the last time, unless some
marvellous inspiration helps me to pitch some plausible yarn."

While he was still harping on the one perpetual theme, the valet
returned with his breakfast, and Melville drank some tea and disposed of
some excellent kidneys.

"I was getting quite faint," he said to the man who was attending to him.
"Don't bother about things this morning. I shall go out presently, and you
can do whatever you've got to do then."

"It's a very wet day, sir," the other answered.

"Wet?" said Melville disgustedly. "I should think it is wet. The weather
certainly means business." He drank some more tea and lighted a cigarette.
"By the way, put out my dress clothes early this evening. I probably shall
not be dining at home."

The valet hesitated.

"Have you any more linen in any other portmanteau, sir?" he asked.

"I'm sure I don't know," Melville replied testily. "You'd better look and
see. Anyhow, find some."

The valet looked still more uncomfortable.

"I sent all I could find to the wash, sir," he stammered; "and the laundry
people have refused to leave any clean linen until your account is settled."

Melville grew scarlet with anger.

"What do I owe them?" he asked.

"It's a little over four pounds, sir. Will you write a cheque?"
 "No, I won't," said Melville shortly. "Go to the Burlington Arcade and
tell my hosiers to send me over three dozen, and put them down in my
account."

"Yes, sir," said the valet civilly, and left the room.

Melville laughed when the door closed behind the servant. When the
devil laughs it is time for good folks to beware, and Melville felt like a
fiend at that moment. It was grotesquely funny that he could get three dozen
shirts on credit, but had not the money to pay his washerwoman. But the
fact was a staggering reminder of his real position. He got up preparatory to
going out, when he remembered that he had still to shave; he went,
therefore, into his bedroom, and, having stropped his razor, took off his
collar and tie and began to make a lather for his face.

And then suddenly the idea came to him with the force of a conviction
that the way out of his trouble lay plain before him. It was the cowardly
way which it yet requires a measure of courage to take. Death was the
solution of the problem. He did not know how to live, but it was very
simple to die. He sat down in a chair and, almost closing his eyes, peered at
his reflection in the mirror. Very little paler—only with eyes quite closed—
he would not look very different presently if he did this thing. And, unless
his courage failed him in the act, it would not hurt. Then what would
happen? The scene here, in this room, with the dead body stretched upon
the floor, was easy to imagine. It might not be very appalling. Had he ever
contemplated such a deed before he would have provided himself with
some poison, which, while it was as fatal as the razor blade, would not
disfigure him; for to the living man the idea of being disfigured after death
is always repugnant. But he had no poison, and here was the razor ready to
his hand. He would be found quite soon—but it must not be too soon—and
he rose and stealthily locked the outer door.

Again he sat before the impassive mirror. There was no one who would
care. In all the world, so far as Melville knew, there was no one who would
care if he were dead, only a few who would resent the manner of his dying.

He had nothing left to lose. Penniless and friendless in the present,

bankrupt of hope for the future, he had nothing material left to lose, at any
rate, and he stood to gain emancipation from an environment to which he
had ceased to be adapted.

He would have to draw the blade across his throat—so! He must do it

very strongly, very swiftly, or he would fail.

The man leant forward on the dressing-table and gazed closely at

himself in the glass; he saw exactly where he must make the gash, and
without any hesitation or nervousness he felt the edge of the razor with the
thumb of his left hand. As he did so he cut the skin, and some blood fell
upon the snow-white cover of the table. In the extraordinary mental state in
which he was, the horrible incongruity in his reasoning did not strike him,
but, in actual fact, the bloodstain on the cloth gave him offence, and he
paused and looked around him. This—would make such a mess! And there
was a revolver in his bag. How stupid of him not to have remembered that!
It had another advantage, too, for people might think the pistol had gone off
by accident while he was cleaning it, whereas there could be no doubt about
the intention in the other case. It mattered a great deal what people would
think.

He laid down the razor on a chest of drawers and removed the soiled
toilet cover from the dressing table. Then he went to his bag to take out his
revolver. The valet had disarranged the contents of the bag, and Melville
turned over a lot of things and could not find the little pistol case. Instead,
his hand fell upon a heap of letters, and on the top of them was the one that
had come to him from Ralph asking for a loan of a hundred pounds.

A sudden revulsion of thought made Melville sick and giddy. It was as

if a gambler who had lost all but his last five-franc piece had, after
hesitation, staked en plein and followed with a run of wins on single
numbers. One cannot follow up the gambler's line of thought, but many a
one whom that fortune befell would be almost sick to think how narrowly
he missed his chance. Melville was a gambler pure and simple. An instant
before he had been upon the very point of death because he did not know
whence money could be got, and without money he did not want to live. Yet
here in his bag was a letter which might mean at least a hundred pounds. Of
course, he might lose his stake, but to kill himself without having made the
venture was intolerable.
 The physical endurance of the strongest man has its limitations, and
Melville staggered into the sitting-room and threw himself into a great
armchair. Here presently he was discovered by his valet, who was
frightened by his master's complete collapse. Some hours passed by before
he regained anything like his usual self-control, and then, resolutely putting
out of his mind all thought of how close he had been to death, he began to
consider the best time and manner of making his final venture to raise
money.

A train left Waterloo at six-forty, which would land him at Fairbridge

Manor at eight o'clock. If he went by that train he would in all probability
find Sir Geoffrey Holt in a good humour after dinner. He even took the
precaution of changing his clothes again, substituting a somewhat shabby
lounge suit for his elaborate frock coat. "May as well look the part," he said
sardonically to himself. "The Prodigal Son was a bit baggy at the knees, I
imagine, and that is the scene I'm on in now. I shall have to draw on my
imagination about the husks all the same."

There was something almost heroic—in a wicked fashion—in his effort

to pull himself together, for his recent temptation to commit suicide had
really shaken him. He drank freely of the spirits in his tantalus as he was
dressing, and all the while tried to anticipate every difficulty in the
interview before him.

"If only Ralph is out of the way I may pull it off. His letter will serve to
account for one hundred of the last two-fifty, and I can gas about some
forgotten bills to explain how most of the rest has gone. It's a fighting
chance anyhow, and if I fail there is still the pistol."

From one thought sprang another.

"There is still the pistol!"

With a curiously furtive action Melville took the revolver from his
portmanteau and slipped it into his pocket. Then he crept downstairs, and,
hailing a hansom, drove to Waterloo.
 But when the train steamed into Fairbridge Station, Melville was not in
it. He was so restless that he could not endure the swaying of the carriage,
and getting out two stations short of his destination he resolved to walk the
rest of the way.

Leaving the high road he made his way down to the river and followed
the towing path. It was getting dark, but the rain had ceased; the silence was
intense, and the occasional splash of a water-rat startled him so much that
he was angry with himself for being in so highly strung and nervous a
condition.

When at last he reached the gardens of the Manor House he was feeling
very shaky; he walked quickly towards the house, wondering, now the
moment was at hand, how he should begin.

"Ralph may be cornered for money," he muttered, "but I notice he hasn't

got rid of his houseboat. I wonder whether he is here to-night. Everything
depends upon that."

He crept cautiously up to the dining-room windows and tried to peep

through the blinds. As he did so he heard the front door open, and crouching
down hid himself in some shrubbery. He recognised Sir Geoffrey's firm,
quick step, and peering over the laurels saw his uncle walking with Ralph
down the drive. He watched them shake hands, and saw Ralph walk briskly
away; then he drew back among the laurels as Sir Geoffrey returned to the
house and quietly closed the door.

"So Ralph is here to-night," said Melville under his breath; "my luck
again!"

He felt horribly uncertain what to do. His first impulse was to follow
Ralph, who might be going up to town, but he refrained, and walked softly
down to the towing path again, turning round at every other step to see if
Sir Geoffrey were coming. The evening grew colder, and Melville turned up
the collar of his coat and stood back among the shadows, steadying himself
against a tree.
 "Perhaps that is Sir Geoffrey," he thought, as the sound of footsteps fell
upon his ear. "No! it's someone going the other way. 'Pon my word, I'm
beginning to feel quite guilty. Still—I'm not going back without seeing him.
Perhaps I'd better go up to the house and get it over. Why can't he come
down here as usual?"

He retraced his steps, and as he reached the garden gate came face to
face with Sir Geoffrey, who, apparently, was not at all surprised to see him.

"How do you do, uncle?" Melville said. "I thought I would look you
up."

"Very good of you, I'm sure," said Sir Geoffrey drily. "Have you just
come from the station?"

"Yes, just this instant," Melville answered, without thinking.

"H'm!" said Sir Geoffrey; "I suppose they must have put on a new down
train. Did you meet Ralph?"

"No," said Melville shortly.

"H'm!" said Sir Geoffrey again; "I thought not."

"Not a very promising beginning!" said Melville to himself; then he

added aloud, "Is Ralph staying with you?"

"He has been," said Sir Geoffrey, "and he's coming back to-morrow, so I
am sorry I cannot offer you his room."

Melville was annoyed.

"I am not aware that I have asked you to give me his room, and I am
aware that you prefer his company."

"That being so," said Sir Geoffrey, "it seems to me that you have chosen
a somewhat unconventional hour for your visit."
 "I've only just returned to England," Melville replied; "otherwise I
should have called earlier."

"May I ask the object of your visit now you have called?" enquired Sir
Geoffrey. "What is it you want?" and he looked keenly at his nephew.

"Well," Melville stammered, "the fact is I wanted to ask you to give me

some more money. I—I——"

"But it's not two months since I gave you two hundred and fifty
pounds," cried Sir Geoffrey. "What on earth have you done with that?"

Melville was at a loss how to begin the explanation he had invented.

"I've been away," he said lamely, "and ill, and—and it's gone."

"I can quite believe it's gone," said his uncle bitterly. "Money melts
before you like pyramids of snow. I wonder you have the face to ask me
again."

Melville flushed. He knew that Sir Geoffrey had detected him in one lie,
and that in his present state of excitement he would only make matters
worse if he faltered in his suddenly improvised story.

"Well, what am I to do?" he asked.

"Do what every other man does," Sir Geoffrey said. "Work, instead of
idling about in the club and playing the fiddle—and the fool."

"But I can't get any work," Melville objected.

"What have you tried to do?"

"Oh, it's no good going into all that."

"I should think not," said Sir Geoffrey with a bitter laugh, "but, anyhow,
I won't help you any more; men of your type never will work while they've
got any relations on whom they can sponge. You give up the fiddle, as a
start."
 "I have," said Melville, "to a pawn-broker."

"Best place for it," grunted Sir Geoffrey unsympathetically. "I'll pay the
interest for you next year, if you'll agree to leave it there."

Melville clenched his fists and walked on in silence for a few yards.

"You don't mind helping Ralph," he said, with a sneer; "he's so different,
isn't he?"

"That is my own affair," Sir Geoffrey said, "but I don't mind saying I've
never had to refuse him, because he has never asked me. He's a thoroughly
fine fellow."

"He's a humbug," said Melville. "He's not above borrowing from me at

all events. As you insist upon knowing what I did with the last two hundred
and fifty I had from you, I will tell you that I gave Ralph a hundred of it."

"I don't believe you," said Sir Geoffrey. "You're a liar, Melville, and I've
proved it."

"Read that," said Melville shortly.

He took Ralph's letter out of his pocket and gave it to his uncle, who
read it in the fading light. A spasm of pain crossed the old man's face, but
he drew himself up with dignity.

"I detected you in one lie, sir," he said, "but I may have made a mistake
about this. If so, I apologise. You did what your brother asked you? Sent
him this hundred pounds?"

Melville met his keen eyes steadily.

"I did. I sent it to him at once."

"How? By cheque?"

"No," said Melville; "in notes—twenty fivers." His wonted effrontery

returned to him. "I can tell you the numbers if you like."
 "Thank you, no," replied Sir Geoffrey. "I'm not proposing to try to trace
the notes now, and Ralph can give me his own explanation of his temporary
embarrassment later. Come to the house and I will repay you for him now."

Melville's heart beat rapidly with excitement. He felt absolutely no

shame at his fraud, no fear of the subsequent inevitable exposure. He had to
get money somehow, and with incredible swiftness it was already almost in
his grasp. They walked in silence to the Manor House. As they passed the
drawing-room windows Melville caught sight of Gwendolen Austen's
figure and involuntarily paused, but Sir Geoffrey noticed the action and
harshly interrupted him.

"Mrs. and Miss Austen are staying here as my guests. As this is purely a
business visit on your part we will, if you please, go to my library," and he
strode along the terrace.

Melville followed him, and turning to the right came to the west front of
the house, on which side lay Sir Geoffrey's private set of rooms. To
Melville, overwrought with excitement as he was, the library with its great
armchairs and well-filled bookcases looked very homelike and comfortable,
but he did not venture to sit down unasked, and Sir Geoffrey pointedly
refrained from everything approaching hospitality. He unlocked a drawer in
his writing table and, taking out his cheque book, filled in a form payable to
Melville for one hundred pounds. Before signing the cheque, he laid down
his pen and looked scrutinisingly at his nephew.

"There are a few things I wish to say to you, Melville," he said very
slowly, "before we finally part, and I beg you to remember them, as they
may prevent any future misunderstanding. For more than thirty years I have
treated you as my son, in spite of endless disappointments at your total
failure to give me any return in consideration or affection. You have always
been utterly selfish, and, as I think, utterly bad. Now I am a rich man, and
you may perhaps argue that I am only anticipating the provision I have
doubtless made for you in my will. Please understand that that is not the
case. Over and above the just expenses of your life up to now you have
already had from me many thousand pounds, which have been squandered
by you in wanton vice. I do not intend you to have any more. I hold that my
money was given to me for some other purpose than that. In point of fact, I
have not made my will, but when I choose to do so, you will not be a
legatee. You understand perfectly?"

Melville bowed.

"Very good. Now I am giving you this cheque because for once you
have done an unselfish action and have lent your brother two-fifths of what
you had reason to suppose was the last money you would ever receive from
me. I am very, very sorry Ralph asked you for it, but very glad you sent it to
him. I repay you on his behalf, and will see that he in turn repays me."

Sir Geoffrey signed the cheque and gave it to Melville.

"I have left it open so that you may obtain the money in the morning.
This, too, is your property," and he gave him Ralph's letter, which Melville
had forgotten.

Then Sir Geoffrey rose.

"This is a final parting, Melville," he said solemnly, "and I wish to

heaven it were not so. If in these last few weeks I had any reason to hope
you had been trying to be a better man I might have been more harsh to-
night, but not so relentless. But the money I gave you the other day, apart
from this hundred pounds, has gone in gambling as all the rest has gone,
and as everything else I might give you would go. And I declare now, upon
my word of honour as a gentleman, that I hold myself free of you at last.
From whatever you may do in the future to bring shame upon your family I,
in their name, declare we are absolved, and you must look for no more help
or countenance from us. And now I will ask you to go. You can walk to the
station, and will not have long to wait for a train to town."

And opening the French windows on to the lawn, Sir Geoffrey stood
with set lips and stern eyes until his nephew disappeared among the
shrubbery that fringed the drive.

Outside, Melville drew a deep breath.

 "The hysterical old idiot!" he said, half audibly; but his fingers trembled
as he placed the cheque in his inner pocket, and he was more nervous than
he thought himself capable of being. "Still, I've got a hundred pounds, and
as for the row which, I suppose, is bound to follow when the old man finds
out the truth—that can rip for the present. I'm glad he didn't cross the
cheque. There wouldn't have been much change out of it for me if I'd had to
pay it into my account, because I'm so overdrawn, and, what's more, it
might be stopped if Ralph turned up early to-morrow. Gad! I'll go to the
bank at nine."

He stumbled along until he reached the station. He had another stiff

glass of spirits at the refreshment bar, and found he had only a shilling left.

"Good thing I took a return ticket," he muttered, "and as for to-morrow I

can go to the bank in a cab, thank goodness, and go home in a balloon, if I
choose. And after that, I'll clear out of town for a bit and pull myself
together—and pull myself together."

He laughed stupidly as he found himself repeating his words, and then

huddled up in a corner of the carriage. How he got back to his chambers in
Jermyn Street he scarcely knew, but he had been there some time before his
attention was attracted by a letter which was lying on his table. It was
written in a hand that was not familiar to him. It bore date that morning, and
the paper was stamped with a monogram and the address, 5, The Vale,
South Kensington.

"Dear Mr. Melville Ashley," it ran, "there are many reasons—into none
of which do I deem it expedient to enter now—why I have hitherto
refrained from inviting you to my house. For the moment I will confine
myself to making the announcement, for which you may be wholly
unprepared, that I married Sir Geoffrey Holt many years ago, and am,
consequently, your aunt by marriage. I shall be obliged if you will call upon
me to-morrow at half-past four o'clock, and it is my desire that until I have
seen you, you shall not acquaint any third person with the contents of this
communication.—I am, yours faithfully, LAVINIA HOLT."
 At last the full significance of the note was borne in upon him.

"Married Sir Geoffrey many years ago!" Melville said slowly. "Strange!
that is very strange!"

He entered the address in his pocket book, and then carefully locked
away the letter, together with that from Ralph, in a despatch box.

"In spite of all you said, Sir Geoffrey, I fancy this letter, too, may mean
money in my pocket!" and the smile upon his face was very evil.

CHAPTER IV.

MEDIATION.

Breakfast is a period of probation for many people's temper. It is a

comparatively easy matter after dinner in the evening to assume light spirits
with one's evening dress, knowing that the work and worries of the day are
all behind one, but considerable philosophy is required to be entirely
amiable the first thing in the morning, when the same work and worries
have to be taken up anew.

So when, the morning following Melville's surprise visit to the Manor

House, Sir Geoffrey entered the dining-room, Gwendolen's loving eyes
perceived at once that something had occurred to ruffle his equanimity.
With her he was never irritable, but his greeting was absent-minded, and he
seemed to seek in vain for anything to interest him in the columns of the
Times.

Mrs. Austen usually breakfasted in bed, and as Ralph was not to return
until the middle of the day, Sir Geoffrey and Gwendolen were alone
together, and the meal passed almost in silence. At last Sir Geoffrey himself
appeared to become aware of the fact that he was discharging his duties as a
host with something less than his usual success.

"Forgive me, Gwen," he said pleasantly. "I'm an old bear this morning,
and poor company for my beautiful princess."

Gwendolen rose and put her arms round his neck.

"Then if the story books are to be believed, the beautiful Princess only
has to kiss the old bear, and he will be transformed into Prince Charming
again," and leaning over him she kissed him affectionately.

"You're a little witch," said Sir Geoffrey, smiling; "but tell me, aren't
you burning to know what has upset my temper to-day?"

"Not at all," Gwendolen answered quickly, "unless it is anything that I

have done."

"Of course it isn't," said Sir Geoffrey; "but it's the next thing to it. I've
got a bone to pick with Ralph."

Gwendolen's face clouded over.

"Oh! I am sorry," she said, but almost immediately her eyes shone
brightly again. "It can't be very serious, though, because he's sure to have
some perfectly satisfactory explanation for whatever he has done, and as
soon as you see him you'll find there's no bone to pick."

"You're a loyal little woman," said Sir Geoffrey, well pleased, "and I've
no doubt you're right. What time is the immaculate hero to honour us by his
reappearance?"

"About a quarter to one," Gwendolen replied.

"In time for luncheon," Sir Geoffrey remarked. "Whatever one may
think about his other meritorious qualities, there can be no doubt about the
excellence of Ralph's appetite."
 "You're trying to draw me," said Gwendolen cheerfully; "but I won't be
drawn. I like a man to have a good appetite, and, by the way, you're not a
bad trencherman yourself."

Sir Geoffrey laughed.

"I've got some work to do this morning," he said as he got up. "You
must kill the time somehow until Ralph returns, and after luncheon you will
be able to pick water lilies and gaze into each other's eyes to any extent. Are
you going to meet him at the station?"

"I thought of doing so," Gwendolen admitted.

"Did you really!" said Sir Geoffrey, with affected incredulity. "Well, I
don't want to interfere with your plans, but seriously, Gwen, as soon as
you've got over the shock—I mean the rapture—of seeing him again, will
you tell him to come to me in the library?"

"Of course I will," said Gwendolen, "and seriously, too, dear uncle, I'm
sure everything will be cleared up as soon as you see him."

"I daresay it will," Sir Geoffrey agreed, "but I have always believed in
getting to the bottom of things immediately. When you're married, Gwen,
avoid a misunderstanding with your husband as you would avoid the devil.
Quarrel if you must, but, at any rate, know what you're quarrelling about.
That's good advice."

"How can an old bachelor give any good advice about the married
state?" Gwendolen asked lightly, and she nodded gaily as she ran upstairs,
not noticing how the expression altered on Sir Geoffrey's face.

"Blows beneath the heart dealt by those one loves the most," he
muttered sadly. "Well, it's inevitable in this world, I suppose, and, after all,
there's compensation in the love itself. But Ralph ought not to have stooped
to borrow that money from Melville; and what on earth can he have wanted
it for that he was afraid to ask me? That's the sting," and the old gentleman
walked slowly to his library and shut himself in there alone.
 Both to Sir Geoffrey and to Gwendolen the morning seemed to drag, but
at last the train which brought Ralph from town arrived, and, heedless of the
bystanders, Gwendolen kissed her lover and walked down the hill with him
to the river.

"Had a happy morning, dear?" he asked.

"A very long one," Gwendolen replied. "Time is very inconsiderate to

people who are in love; it flies when they are together and halts when they
are alone, whereas, of course, it ought to do exactly the reverse."

"Of course it ought," Ralph assented, "but, anyhow, it's ripping to be

alive. By Jove, Gwen, I think I'm the happiest man in the whole world."

Gwen looked at him critically.

"I'm sure you are the nicest," she said enthusiastically, and did not
demur to his finding her approval an excuse for another kiss.

"Let's go on the houseboat," he said, "and after luncheon I will punt you
up to where the water lilies are."

"Pick water lilies and gaze in each other's eyes," said Gwen, laughing;
"that was the programme Sir Geoffrey mapped out for us. Oh! I forgot. He
asked me to send you to him directly you arrived. He's in the library."

"Can't it keep till after luncheon?" Ralph asked indifferently. "I want to
talk to you."

"No," Gwen replied; "you must go now. I promised that you would. He
said he had a bone to pick with you."

"Did he?" said Ralph. "I wonder what's the matter."

"I don't know," Gwen answered, "but he was very quiet at breakfast, and
I guessed there was something wrong; then he told me it was about you, and
I said you could explain anything you did or didn't do, and you've got to go
at once and do so."
 "A very lucid statement," Ralph said, smiling. "Well, it's a bore to have
to leave you at once, but if you've promised, there's no help for it."

"None," said Gwendolen gravely. "Come along, Ralph."

In her heart she was a little uneasy, for although she had absolute
confidence in Ralph's perfect integrity, she had never before seen Sir
Geoffrey look so troubled at anything in which his favourite nephew was
concerned. But she stifled her not unnatural curiosity, and, leaving Ralph at
the library door, ran off to the room where her mother was writing wholly
unnecessary letters.

Sir Geoffrey was so engrossed in a book that he did not hear Ralph
come into the room. Comfortably ensconced in a huge armchair, with
spectacles on his nose, and the sunlight streaming through the window upon
his silver hair, he embodied the general idea of a cultivated old English
gentleman. Ralph looked at him, and then spoke.

"Gwendolen tells me you want to see me, Uncle Geoffrey, so I've come
straight in."

Sir Geoffrey looked up.

"Yes," he said. "Melville was here last night."

Ralph was vexed, for he knew what was the usual reason for his
brother's visits to Fairbridge.

"Was he?" he said. "I didn't know he was back."

"Then you knew he was going abroad?"

"Oh, yes," said Ralph. "He made no secret about it to me."

Sir Geoffrey only grunted, and Ralph went on.

"In many ways I'm rather sorry for Melville, uncle. Of course, I know
he has been a lot of worry to you, but he's my brother after all, and it isn't
easy to get the sort of work that he could do."
 "He's had a good education," said Sir Geoffrey, "and he's got good
health and a pair of hands. What more does a man need to earn an honest
living?"

Ralph was very happy, and when one is happy it is difficult not to feel
generously disposed even to those one loves the least; so now he
championed his brother quite sincerely.

"I've got all that, too," he said, but Sir Geoffrey put up his hand in
deprecation of any comparison between the two brothers.

"You owe me a hundred pounds, Ralph," he said.

"My dear uncle," Ralph replied. "I owe you a great deal more than that.
I can never repay you a fraction of what I owe you."

Sir Geoffrey's face lighted up with pleasure at the young fellow's frank
expression of gratitude.

"One does not repay free gifts," he answered. "Let all that pass; but,
Ralph, why couldn't you tell me you were in need of ready money?"

"I don't quite understand," said Ralph, looking puzzled.

"A few weeks ago," said Sir Geoffrey, rather testily, "you borrowed it
from Melville, and I repaid him for you last night."

Ralph's face flushed with indignation.

"You paid Melville a hundred pounds for me?"

"Yes," said his uncle.

"But I don't owe him anything."

"You wrote to him at Monte Carlo, and asked him for a hundred pounds.
What did you want that for?"