US3730389A

US3730389A - Syringe

Info

Publication number: US3730389A
Application number: US00155570A
Authority: US
Inventors: R Harris
Original assignee: PRECISION SAMPLING CORP
Current assignee: PRECISION SAMPLING CORP
Priority date: 1971-06-22
Filing date: 1971-06-22
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01

Abstract

An improved syringe for dispensing accurately measured quantities of fluid specimens. It comprises a unique plunger and plunger guide assembly, adapted for engagement with a pair of ferrules fitted upon a syringe barrel, in addition to the usual combination of a barrel and a hollow or tubular needle mounted on the forward end of the barrel such that the axial opening of the barrel and the needle opening are communicated to provide a continuous bore. A pair of ferrules, each provided with a plurality of openings (preferably two) of equal number, are fitted upon the barrel, one to the rear and one to the front of the barrel. The openings of the ferrules are aligned. The forward ferrule is adjustably movable upon the barrel, while the other is fixed. The rearward ferrule is provided with openings which subtend a larger arc distance than those of the forward ferrule. The plunger guide, a sub-component of a plunger assembly, comprising a plunger and a plunger guide, is mounted upon the barrel for slidable engagement therewith, via projections corresponding to the number of openings within the ferrules, which are extended through the openings of the rearward ferrule. In one position the terminal ends of members located on the plunger guide will impinge on the front ferrule, this corresponding with a pre-selected setting of the volume of a fluid specimen to be delivered, and in another position the entire plunger assembly can be partially rotated upon the barrel and within the openings of the rear ferrule so that the members of the plunger guide can pass through the openings of the forward ferrule such that the plunger can then be pushed forward to deliver the fluid specimen through the needle.

Description

llnited States Patent 11 1 Harris, Sr. et al.

[ SYRHIGE [76] lnventors: 1151.6 J. Harris, Sr., 9880 S. Liveroaks Drive; Rano J. Harris, .112, 1945 Carolyn Sue Drive, both of Baton Rouge, La. 70815 22 Filed: June 22, 1971 211 Appl. No.: 155,570

[52] U.S. Cl. ..222/31, 128/218 C, 128/234,

222/386 [51] Int. Cl. ..B67d 5/22 [58] Field of Search ..222/3l, 326, 327,

218C, 218 D, 218 P, 218 PA, 219, 220, 234,

An improved syringe for dispensing accurately measured quantities of fluid specimens. It comprises a unique plunger and plunger guideassembly, adapted 14 1 May 1,1973

for engagement with a pair of ferrules fitted upon a syringe barrel, in addition to the usual combination of a barrel and a hollow or tubular needle mounted on the forward end of the barrel such that the axial opening of the barrel and the needle opening arecommunicated to provide a continuous bore. A pair of ferrules, each provided with a plurality of openings (preferably two) of equal number, are fitted upon the barrel, one to the rear and one to the front of the barrel. The openings of the ferrules are aligned. The forward ferrule is adjustably movable upon the barrel, while the other is fixed. The rearward ferrule is provided with openings which subtend a larger arc distance than those of the forward ferrule. The plunger guide, a sub-component of a plunger assembly, comprising a plunger and a plunger guide, is mounted upon the barrel for slidable engagement therewith, via projections corresponding to the number of openings within the ferrules, which are extended through the openings of the rearward ferrule. In one position the terminal ends of members located on the plunger guide will impinge on the front ferrule, this corresponding with a pre-selected setting of the volume of a fluid specimen to be delivered, and in another position the entire plunger assembly can be partially rotated upon the barrel and within the openings of the rear ferrule so that the members of the plunger guide can pass through the openings of the forward ferrule such that the plunger can then be pushed forward to deliver the fluid specimen through the needle.

12 Claims, 7 Drawing Figures PATENTEB MAY 1 I975 IINVENTORS RANO J. HARRIS, SR. RANO'J. HARRIS, JR.

ig QMGQD. C1 TTORNEY SYRINGE Syringes have gained wide acceptance by the industry, and by the scientific community, generally, for use in dispensing infinitesimally small, accurately measured fluid specimens, e.g., to modern analytical instruments such as mass spectrometers and gas chromatographs. Such syringes embody apparatus comprising a tubular body or barrel, on the forward end of which is fitted a hollow or tubular needle and, at the opposite end, a slidable plunger which travels within the barrel. In the most accurate of existing syringes, the measured fluid is dispensed by the positive action of a very small diameter wire plunger which travels the length of the barrel. Syringes of this character are capable of dispensing very small fluid specimens measured on the order of very small fractions of a microliter.

The syringe embodied by the present invention provides further improvements over prior art devices.

Among the objects of this invention are:

To provide a new and improved syringe capable of more rapidly measuring out infinitesimally small, accurately measured fluid specimens, particularly fractional incrementsof liquid representative of the total volumetric capacity of a given syringe.

To provide a syringe of simple structure which can be repetitively filled to a pre-selected setting, with precision and accuracy, and the fluid specimen then injected with similar precision and accuracy To provide a syringe particularly adapted for the precise measurement of liquids without significant error introduced by paralax, as often occasioned by inaccurate observations of the location of a very fine plunger tip in relation to scribed indicia marks.

To provide a syringe having a plunger which can be adjusted to the length of the bore, and to the zero marking, by very simple manual manipulations.

To provide a more durable syringe of simple structure, particularly one wherein there are no complicated alignments to be made between the plunger tip and the end of the needle, whereat it enters into the barrel, such as can cause excessive wear and create maintenance difficulties.

These and other objects are achieved in accordance with the present invention which embodies improvements in syringes comprising the usual combination of a tubular member or barrel within the forward end of which is provided a hollow or tubular needle, and within the opposite end of which is fitted. a wire plunger, reciprocably mounted within the bore of the barrel. In the improved combination, a pair of ferrules, each provided with a plurality of openings between the respective member and the external surface of the wall which forms the barrel, are located upon the barrel, one to the rear and one to the front of the barrel. In normal operative position the front ferrule is adjustable, and the trailing edge thereof can be set to correspond to a desired scale setting. The openings of both the front and rearward ferrules are aligned one upon the other, and the openings of the rearward ferrule, which in normal operation is located in a fixed position off the scale of the barrel, is slightly off-set or subtends a wider arc length than those of the front ferrule. The plunger assembly, which includes both a plunger guide and plunger, is of special design and is adapted to work in combination with the said pair of ferrules located on the barrel.

The plunger guide is comprised of a member upon which is mounted a plurality of projecting fingers or branches alternately disposed in circular pattern, the number corresponding with the number of openings within the ferrules, and the inner faces of which are curved to correspond substantially with the curvature of the barrel upon which they are fitted for slidable engagement. In a preferred design the plunger guide is formed from a tubular sleeve, the wall of which is deeply notched from its forward end by a pair of op positely disposed notches to provide a pair of branches which project from a tubular wall segment. The tubular wall segment is threadably adapted to receive a plunger. A preferred feature of the invention is that it provides a zero plunger adjustment. A small tubular member, or adjustable stop, can also be mounted on the plunger forward of the said threaded plunger portion and within the tubular wall segment to provide a means for adjustment of the length of the wire plunger which extends into the bore of the barrel. In position,

the projecting surfaces of the plunger guide are extended through the openings of the rearward ferrule and span the barrel, the wire portion of the plunger is mounted within the bore of the barrel, and the whole of the plunger assembly is reciprocable, and rotatable to a limited extent within the openings of the rearward ferrule. In one position the terminal ends of the projecting members of the plunger guide will contact or impinge upon the front ferrule, the trailing edge of this member being pre-set to provide a measured volume of a fluid specimen to be delivered through the needle and, in another position, the entire plunger assembly can be partially rotated upon the barrel and within the openings of the rearward ferrule so that the projecting members of the plunger guide can enter the openings of the front ferrule and pushed forward to deliver the indicated amount of fluid specimen through the needle.

The invention, and its principle of operation, will be more fully understood by reference to the following detailed description of a specific embodiment, and to the attached drawings to which reference is made in the description. In the description, similar numbers are used to represent similar parts or components, and subscripts are used where there are a plurality of similar parts or components.

In the drawings:

FIG. 1 is a perspective view, depicted in exploded fashion, of a preferred type of syringe embodying the present invention;

FIG. 2 is a perspective view of the syringe of the preceding figure in assembled form;

FIGS. 3-5, by reference to a progressive series of fragmentary views of the forward end of the assembled syringe, depict a sequence describing injection of a specimen;

FIG. 6 is a section taken on the line 6-6 of FIG. 2; and

FIG. 7 is a section taken on line 7-7 of FIG. 2.

Referring to the drawings, particularly to FIG. 1, there is shown a syringe indicated generally by the numeral 10. The syringe 10 includes generally a hollow barrel or tubular body 11, provided by an enclosing wall which defines a central axial opening or bore. In its preferred form the barrel 1 1 is formed of glass or transparent plastic, most preferably the former, and outwardly scribed with indicia marks representative of the volume of the bore. A cannula or tubular needle 12 is tightly mounted, and sealed within the forward end of the barrel 11, the bore of the needle being aligned upon the axial opening or bore through the center of the barrel 11. A plunger assembly, comprised generally of a plunger guide 21 and plunger 32, is mounted at the rearward end of the barrel 11, the plunger 32 being reciprocably movable through the bore of the barrel.

The plunger guide 21 can be constructed as a unitary member, described generally as a cylindrical member with deeply slotted sides 21 ,22 which, in effect, provide a tubular segment and a pair of alternately disposed

guide members

23 ,23 In all embodiments a plurality of guide members 23 are provided, the inside curvature of a guide member substantially corresponding with the outside curvature of the wall which forms the barrel 11 so that the plunger guide 21 can grasp and freely slide upon the barrel 11 as the plunger 32 is reciprocated within the bore of the barrel 11. The closed end or tubular segment of the plunger guide 21 is internally threaded, and the threads 24 adapted for threadable engagement with the externally threaded shank portion 31 of plunger 32 so that both the plunger guide 21 and plunger 32 are held in fixed relationship, one with respect to the other, when the syringe is assembled. The plunger guide 21 can be constructed of essentially any rigid or semi-rigid material, but preferably is constructed of metal such as aluminum, ferrous metals or their alloys, and the like.

The plunger 32 is constructed of wire of very thin cross-sectional diameter, and the forward end or tip 36 thereof can be capped by a highly preferred type of stress formed seal, e.g., a Teflon seal, such as described in U.S. Pat. No. 3,577,850 which issued May ll, 1971, herewith incorporated by way of reference. A thumb button 33 is located upon the opposite end of the plunger 32, the thumb button 33 being adjoined to the plunger wire via the threaded projections or

shank portions

31,34. The threaded shank 31 mates with internal threads 24 of the plunger guide 21 so that the plunger guide 21 and plunger 32 are held in fixed relationship, one member with respect to the other, when the syringe is assembled. The internally threaded cylindrical or tubular member 35 in combination with the threaded shank portion 34 of the plunger 32 provides a means of adjustment by virtue of which the tip 36 of the plunger can be conveniently set at the zero filling mark, this point generally being just barely short of the terminal end of the needle 12. This is accomplished by setting the distance within which the plunger can be extended into the bore of the barrel 1]. The tubular member 35 is thus a plunger stop which is adapted to fit tightly in position near the rearward end of plunger 32, but yet sufficiently loose as to be movable between adjustments. A tight fit wherein the diameter of the wire plunger exceeds the internal diameter by about 0.001 inch is generally adequate. Preferably, the tubular member 35 is adapted for threadable engagement with the external threads of smaller diameter shank portion 34 of plunger 32, such that rotation of the tubular member 35 relative to the shank 34 will produce movement of the tubular member 35 in one of the two possible directions along the shank. If the tubular member 35 is thus threaded such that when rotated it will move toward the tip 36 of plunger 32, the length of the wire portion of the plunger that can be extended through the bore of barrel 11 will be shortened. Conversely, if the tubular member 35 is rotated such that it is moved in the opposite direction, the effective length of the wire portion of the plunger will be lengthened. Setting the tip 36 of the plunger 32 just short of contact with the terminal end of the needle 12, where it enters into the bore of barrel 11, prevents damage to the plunger tip and prevents packing of infinitesimally small solid contaminants into the needle opening. I

In assembled position, as best shown by reference to FIG. 2, the pair of

plunger guide members

23 ,23 are passed through

openings

14 ,14 of the bushing or ferrule 13 which is fixed upon the rearward end of barrel 11, the inside faces thereof being fitted to the curvature of the outside wall of the said barrel for reciprocable slidable movement thereon. The ferrule 13 is positioned and held tightly in place upon barrel 11 by a threaded bolt or screw 15 which is fitted through a threaded tap for physical contact of the end thereof with the side wall of barrel 1 l. The ferrule 16, also provided with a pair of

openings

17 ,17 through which the

plunger guide members

23 ,23 can be passed, is similarly positioned and held tightly in place upon the forward end of barrel 11. The arc subtended by the

openings

17 ,17 is somewhat less than that subtended by the the

openings

14 ,14 of fixed ferrule 13. The position of the forward ferrule 16 is normally adjusted, during the various operations, with its trailing edge upon the precise volume of specimen, as represented by the indicia mark with which it corresponds, which is to be delivered through the dispensing end of the needle 12.

In describing a specific operation, it is supposed, for example, that the tip 36 of plunger 32 has been set to flush with the zero mark, that a screw 18 of forward ferrule 16 have been loosened and the ferrule 16 moved such that its trailing edge is aligned upon the indicia mark representing 2 microliters, this setting corresponding to a bore volume between the readings zero and two" or two microliters. The bolt or screw 18 is then tightened into place so that the end and at thereof contacts the outside wall of barrel 11 and prevents relative movement between barrel 11 and ferrule 16. The amount of the fluid specimen desired to be injected then is 2 microliters and somewhat more than this volume of a specimen has been withdrawn from a source (not shown), and the setting of the instrument then is as described by reference to FIG. 2. Referring to FIG. 3, the plunger 32 is pushed forward until the terminal ends of the

plunger guide members

23 ,23 come into contact with the trailing edge of forward ferrule 16. Liquid specimen in excess of two microliters is thus rejected, any residual specimen is wiped from the dispensing end of the needle 12, and the syringe is ready to inject the 2 microliters of specimen into, e.g., the septum of a modern analytical instrument, such as a mass spectrometer or gas chromatograph for chemical analysis.

To accomplish injection of the two microliter specimen, the plunger assembly is rotated counterclockwise so that the terminal ends of

plunger guide members

23 ,23 are aligned upon the

openings

17 ,17 of the forward ferrule 16 as shown by reference to FIG. 4. It is to be noted that thearc lengths of

openings

14 ,14 of ferrule 13 are sufficiently great as to permit this slight rotation of the plunger assembly upon barrel ii 1. For delivery or injection of the accurately measured 2 microliter specimen, the plunger 32 is then pushed forward such that the specimen is expelled by the positive action of the plunger as shown by reference to FIG. 5.

The relative sizes, and locations, of

openings

14 ,14 of fixed ferrule 13 and

openings

17 ,17 of movable ferrule 16 and the angles subtended by thearcuate lengths of the respective openings are readily observed by reference to FIGS. 6 and 7. It is seen, by comparisons of these figures, that sufficient space is provided within the 'left side of

openings

14 ,14 that the plunger assembly can be readily shifted by counter-clockwise rotation and, in so doing, that the pair of

plunger guide members

23,,23 can be aligned upon

openings

17 ,17 so that they can be passed therethrough when the plunger is moved forward.

A prime purpose of the

plunger guide members

23 ,23 is to maintain alignment of, and to guide the thin wire plunger 32 through, the continuous bore of the barrel 1 1. An important feature of the design of this syringe, however, including particularly the design of the plunger guide assembly, is that paralax can be virtually eliminated from syringe readings. In preferred embodiments, the

plunger guide members

23 ,23 are of equal length and the terminal ends of

plunger guide members

23 ,23 are precisely aligned, one with the other, and upon the extreme terminal forward end of tip 36 of the plunger 32. By precisely aligning these three reference points, an exact reading can be taken at any scale location on the barrel 11. It is preferred also that at the zero mark all three of these reference points are precisely aligned upon zero.

It is apparent that various modifications and changes can be made without departing the spirit and scope of the present invention. The apparatus is constructed of materials substantially inert or non-reactive to the chemical or corrosive action of the fluid specimens to be measured and dispensed. The barrel is normally constructed of glass, but can be constructed of a plastic or plastic-like material. The forward seal located on the plunger tip and the tubular member used to adjust the limits of the plunger stroke are normally constructed of plastic, and the rest of the syringe of various metals.

The tubular member and the seal are preferably formed of a rigid or semi-rigid, resilient form of plastic or plastic-like material. The self-lubricated plastics are especially preferred in this capacity, and can also be applied as a laminate or protective film. The polyfluorinated ethylene polymers, notable among which is polytetrafluoroethylene (Teflon), are particularly outstanding. Conventional resilient or elastic-like materials, such as natural or synthetic rubbers, can also be employed.

The plunger assembly and the needle of the syringe are preferably constructed of metals, e.g., ferrous metals such as iron, iron alloysQsteel, stainless steels, and the like; or such metals as aluminum, magnesium, brass, copper, bronze, chrome, alloys of these and other metals, and the like.

It is apparent that various changes, such as in the absolute or relative dimensions of the parts, materials used, and the like, as well as the suggested mode of withdrawing or delivering fluids, can be made without departing the spirit and scope of the invention, as will be apparent to those skilled in this art.

Having described the invention, what is claimed is:

1. In a syringe for dispensing small, accurately measured quantities of fluid specimens, the combination comprising a barrel formed by an enclosing wall defining an axial opening,

a hollow needle mounted at the forward end of the barrel, the opening through the said needle communicating with the axial opening through the barrel,

a pair of ferrules, each containing a central opening forming a ring through which the barrel is slidably fitted, a plurality of openings within the ring portion of each of the ferrules, a first ferrule being located toward the rear of the barrel while a second ferrule, located in front of the first ferrule, can be adjustably located in different positions along the length of the barrel, the arc lengths of the openings within the ring portion of the first ferrule being greater than that of the openings within the ring portion of the second ferrule upon which they are aligned,

a plunger assembly including a plunger guide and plunger, said plunger guide including a tubular member, the

wall of which is cut away from the forward end by a plurality of deep slots to provide a tubular segment and a plurality of alternately disposed projecting plunger guide members, corresponding in number with the number of openings within the ring portions of the said ferrules, the inside faces of each of which are curved to correspond substantially with the outside curvature of the wall which forms the barrel so that these members can grasp and freely slide upon the external. wall of the barrel, said plunger including a shank portion which is operatively engaged to the tubular segment of the plunger guide, whereby, in assembled position, the plunger guide members are located within and pass through the openings of the first ferrule, the plunger is maintained in alignment with and reciprocably movable within the axial opening of the barrel, and wherein, in one position, the terminal ends of the plunger guide members will impinge upon the second ferrule, this correspond ing to a preselected setting of a volume of a fluid specimen to be delivered through the needle and, in another position, the entire plunger assembly can be partially rotated upon the barrel and within the openings within the ring portion of the first ferrule so that the terminal ends of the plunger guide member can pass through the openings within the ring portion of the said second ferrule and the plunger then pushed forward to deliver the said accurately measured volume of the fluid specimen.

2. The apparatus of claim 1 wherein two openings are contained within each of the ferrules, and two oppositely disposed plunger guide members are contained within the plunger guide.

3. The apparatus of claim I wherein the tubular segment of the plunger guide is internally threaded and the plunger is provided with an externally threaded shank, such that the tubular segment and plunger can be threadably engaged, one member to the other.

4. The apparatus of claim 1 wherein the tubular segment of the plunger guide is internally threaded, the plunger is provided with an external shank of two different diameters, the smaller diameter shank being contiguous to the terminal end of the plunger and adapted to receive a tubular member of smaller external diameter than that of the opening within the tubular segment of the plunger guide while the larger diameter shank is externally threaded and thereby adapted for threadable engagement with the internally threaded tubular segment of the plunger guide, and wherein the said tubular member for location on the smaller diameter shank portion of the plunger is movable thereon so that the length of the plunger can be adjusted.

5. The apparatus of claim 4 wherein a thumb button is attached upon the larger diameter shank portion of the plunger.

6. The apparatus of claim 4 wherein the smaller diameter shank portion of the plunger is externally threaded and the tubular member adapted for movement thereon is internally threaded for threadable engagement therewith.

7. The apparatus of claim 6 wherein the tubular member consists essentially of Teflon.

8. The apparatus of claim 1 wherein the barrel is comprised of glass, and indicia marks are scribed thereon.

9. The apparatus of claim 1 wherein the ferrules are comprised of Teflon, adjustably secured in place upon the wall of the barrel by bolts.

10. The apparatus of claim 1 wherein the forward tip of the plunger is capped with a seal.

11. In a syringe for dispensing small, accurately measured quantities of fluid specimens, the combination comprising a barrel formed by an enclosing wall defining an axial opening,

a pair of ferrules, each containing a central opening forming a ring through which the barrel is slidably fitted, a pair of alternately disposed slot-like openings within the ring portion of each of the ferrules, a first ferrule being located toward the rear of the barrel while a second ferruleflocated in front of the first ferrule and on the forward end of the barrel, can be adjustably moved and located in different positions along the length of the barrel, the arc lengths of the pair of slot-like openings within the ring portion of the first ferrule being greater than that of the pair of slot-like openings within the ring portion of the second ferrule upon which they are aligned, a plunger assembly including a plunger guide and plunger, said plunger guide including a tubular member, the wall of which is cut away from the forward end by a pair of alternately disposed deep slots to provide a tubular segment, the inside surface of which is threaded, and a pair of alternately disposed pro ecting plunger guide members, the

width of each of which is lesser than that of either of the slot-like openings within the ring portion of both the first and second ferrule, and the inside faces of each of the plunger guide members are curved to correspond substantially with the outside curvature of the wall which forms the barrel so that these members can grasp and freely slide upon the external wall of the barrel, said plunger including a shank portion, a small diameter externally threaded forward portion, and a larger diameter externally threaded portion which is threadably engaged to the said tubular segment of the plunger guide, an internally threaded tubular member of diameter greater than that of the axial opening through the barrel located on the externally threaded smaller diameter shank portion of the plunger, and axially movable thereon, so that the length of the plunger which can be extended into the axial opening of the barrel can be adjusted, whereby, in assembled position, the plunger guide members are located within and pass through the openings of the first ferrule, the plunger is maintained in alignment with and reciprocably movable within the axial opening of the barrel, and wherein, in one position, the terminal ends of the plunger guide members will impinge upon the ring portion of the second ferrule, this corresponding to a preselected setting of a volume of a fluid specimen to be delivered through the needle and, in another position, the entire plunger assembly can be partially rotated upon the barrel and within the openings within the ring portion of the first ferrule so that the terminal ends of the plunger guide member can pass through the openings within the ring portion of the said second ferrule and the plunger then pushed forward to deliver the said accurately measured volume of the fluid specimen. 12. The apparatus of claim 11 wherein the internally threaded member is constructed of Teflon, the barrel is comprised of glass with indicia marks scribed thereon, the ferrules are constructed of Teflon, adjustably secured in place upon the wall of the barrel by bolts, and the forward tip of the plunger is capped with a Teflon seal.

Claims

1. In a syringe for dispensing small, accurately measured quantities of fluid specimens, the combination comprising a barrel formed by An enclosing wall defining an axial opening, a hollow needle mounted at the forward end of the barrel, the opening through the said needle communicating with the axial opening through the barrel, a pair of ferrules, each containing a central opening forming a ring through which the barrel is slidably fitted, a plurality of openings within the ring portion of each of the ferrules, a first ferrule being located toward the rear of the barrel while a second ferrule, located in front of the first ferrule, can be adjustably located in different positions along the length of the barrel, the arc lengths of the openings within the ring portion of the first ferrule being greater than that of the openings within the ring portion of the second ferrule upon which they are aligned, a plunger assembly including a plunger guide and plunger, said plunger guide including a tubular member, the wall of which is cut away from the forward end by a plurality of deep slots to provide a tubular segment and a plurality of alternately disposed projecting plunger guide members, corresponding in number with the number of openings within the ring portions of the said ferrules, the inside faces of each of which are curved to correspond substantially with the outside curvature of the wall which forms the barrel so that these members can grasp and freely slide upon the external wall of the barrel, said plunger including a shank portion which is operatively engaged to the tubular segment of the plunger guide, whereby, in assembled position, the plunger guide members are located within and pass through the openings of the first ferrule, the plunger is maintained in alignment with and reciprocably movable within the axial opening of the barrel, and wherein, in one position, the terminal ends of the plunger guide members will impinge upon the second ferrule, this corresponding to a preselected setting of a volume of a fluid specimen to be delivered through the needle and, in another position, the entire plunger assembly can be partially rotated upon the barrel and within the openings within the ring portion of the first ferrule so that the terminal ends of the plunger guide member can pass through the openings within the ring portion of the said second ferrule and the plunger then pushed forward to deliver the said accurately measured volume of the fluid specimen.

3. The apparatus of claim 1 wherein the tubular segment of the plunger guide is internally threaded and the plunger is provided with an externally threaded shank, such that the tubular segment and plunger can be threadably engaged, one member to the other.

11. In a syringe for dispensing small, accurately measured quantities of fluid specimens, the combination comprising a barrel formed by an enclosing wall defining an axial opening, a hollow needle mounted at the forward end of the barrel, the opening through the said needle communicating with the axial opening through the barrel, a pair of ferrules, each containing a central opening forming a ring through which the barrel is slidably fitted, a pair of alternately disposed slot-like openings within the ring portion of each of the ferrules, a first ferrule being located toward the rear of the barrel while a second ferrule, located in front of the first ferrule and on the forward end of the barrel, can be adjustably moved and located in different positions along the length of the barrel, the arc lengths of the pair of slot-like openings within the ring portion of the first ferrule being greater than that of the pair of slot-like openings within the ring portion of the second ferrule upon which they are aligned, a plunger assembly including a plunger guide and plunger, said plunger guide including a tubular member, the wall of which is cut away from the forward end by a pair of alternately disposed deep slots to provide a tubular segment, the inside surface of which is threaded, and a pair of alternately disposed projecting plunger guide members, the width of each of which is lesser than that of either of the slot-like openings within the ring portion of both the first and second ferrule, and the inside faces of each of the plunger guide members are curved to correspond substantially with the outside curvature of the wall which forms the barrel so that these members can grasp and freely slide upon the external wall of the barrel, said plunger including a shank portion, a small diameter externally threaded forward portion, and a larger diameter externally threaded portion which is threadably engaged to the said tubular segment of the plunger guide, an internally threaded tubular member of diameter greater than that of the axial opening through the barrel located on the externally threaded smaller diameter shank portion of the plunger, and axially movable thereon, so that the length of the plunger which can be extended into the axial opening of the barrel can be adjusted, whereby, in assembled position, the plunger guide members are located within and pass through the openings of the first ferrule, the plunger is maintained in alignment with and reciprocably movable within the axial opening of the barrel, and wherein, in one position, the terminal ends of the plunger guide members will impinge upon the ring portion of the second ferrule, this corresponding to a pre-selected setting of a volume of a fluid specimen to be delivered through the needle and, in another position, the entire plunger assembly can be partially rotated upon the barrel and within the openings within the ring portion of the first ferrule so that the terminal ends of the plunger guide member can pass through the openings within the ring portion of the said second ferrule and the plunger then pushed forward to deliver the said accurately measured volume of the fluid specimen.

12. The apparatus of claim 11 wherein the internally threaded member is constructed of Teflon, the barrel is comprised of glass with indicia marks scribed thereon, the ferrules are constructed of Teflon, adjustably secured in place upon the wall of the barrel by bolts, and the forward tip of the plunger is capped with a Teflon seal.