WO1997011728A1

WO1997011728A1 - Non-reusable syringe with removable plunger usable as a needle guard

Info

Publication number: WO1997011728A1
Application number: PCT/US1995/012281
Authority: WO
Inventors: Roy Hammett; Eric J. Sundsvold
Original assignee: Roy Hammett; Sundsvold Eric J
Priority date: 1995-09-25
Filing date: 1995-09-25
Publication date: 1997-04-03
Also published as: AU3641995A

Abstract

A disposable hypodermic syringe (10) having a barrel (11) with an adapter (13) on one end for attachment of a needle (14), a piston (17), and plunger (16) reciprocable in the barrel. The plunger (16) has a longitudinally extending hollow bore (30, 90) therein, is removable from the barrel, and lockable on the adapter in enclosing relationship to the needle to serve as a needle guard. A quantity of adhesive (51) may be provided in the plunger to be pierced by the needle when the plunger is placed over the needle to serve as a needle guard, thereby permanently fixing the plunger/guard to the needle. The piston (17) is releasably attached to the plunger by pivotable latch arms (21, 22) on the plunger that engage around pivotable latch fingers (18) on the piston to hold the latch fingers engaged behind a retaining ring on the plunger and thus hold the piston to the plunger.

Description

NON-REUSABLE SYRINGE WITH REMOVABLE PLUNGER USABLE AS A NEEDLE GUARD

Technical Field of the Invention:

This invention relates generally to hypodermic syringes, and more particularly, to an inexpensive hypodermic syringe that is capable of use only once, and which has a part that is removable after use to serve as a needle guard. The invention represents an improvement over the syringes shown in earlier patent numbers 5, 1 81 ,91 2, 5,352,200 and 5,352,202.

Background of the Invention:

It is frequently necessary to use hypodermic syringes for intravenous administration of fluids, or to withdraw fluids from the veins of a person during the course of treatment of an illness, or in routine diagnostic examinations. Hypodermic syringes used for this purpose are generally disposable, and are intended to be discarded after a single use by trained medical personnel.

Unless they are properly disposed of, these used syringes present a health hazard. One of the more serious concerns of health care workers is the danger of becoming accidentally infected with HIV-infected blood or other materials. Acquired Immune Deficiency Syndrome (AIDS) is now recognized as an epidemic of global proportion. In addition, there is an increasing recognition of a broad spectrum of severe HIV-associated diseases, including pneumonia, endocarditis, and pulmonary tuberculosis. Medical and rescue personnel are aware of these risks, and when possible, take precautions to avoid unnecessary exposure or contact with infectious materials.

However, if a used syringe has been left intact and not properly disposed of, medical and rescue personnel, custodial workers, and others, are exposed to the danger of being accidentally pricked with the contaminated needle in spite of the precautions that they might normally take. Such a needle could be mingled with soiled linens, bandages or other materials, and when these materials are gathered for disposal, the needle has the distinct potential of penetrating the skin of anyone handling the materials.

The used syringe could also fall into the hands of a drug addict or other person who may be inclined to reuse the syringe. Such persons typically reuse a syringe many times and share it with other addicts. If the syringe has been used to make an injection or to withdraw body fluid from a person having an infectious disease, all of those persons subsequently using the contaminated needle are at risk of acquiring the infectious disease.

To prevent such accidents from occurring, the needles should be broken from the used syringes, and/or encased in a protective sheath, and devices have been provided in the prior art for accomplishing this. For instance, needles have been joined to the syringe body through frangible connections so that the doctor, nurse or other medical personnel can easily break the needle from the syringe after it is used. Unfortunately, this is not always done during the urgency of medical treatment, or if it is, there still remains an exposed needle body.

Similar shortcomings exist with respect to guards or sheaths that have been provided to encase the used needle. Such guards generally comprise separate sleeves or cap members that enclose the needle before it is used and which must be removed and set aside during use of the syringe. It is intended that after use of the needle, the guard will again be placed over the needle. However, the guard may become misplaced during the medical procedure being performed and therefore not available for reuse. Even if it is not misplaced, the person responsible for safe handling of the syringe may not have the time, or take the time, to retrieve the guard and place it over the needle. Further, even if such a conventional guard is placed on the needle, it is capable of being removed, whereby the syringe could again be rendered capable of use.

In addition to an effective needle guard for used syringes, a means is needed to prevent sharing and reuse of syringes, and thereby to prevent the spread of infectious diseases caused by use of contaminated syringes. A significant preventive measure would be the provision and use of syringes that could be used one time. Accordingly, it would be desirable to have a disposable hypodermic syringe that is reliable in operation, simple and economical in construction, and in which a part of the syringe assembly itself is adapted as a needle guard after the syringe has been used for its intended purpose. It would further be desirable to provide a disposable syringe that is not capable of being reused after a single use.

Summary of the Invention:

The disposable syringe of the invention comprises a cylindrical syringe barrel of substantially conventional construction, having an open end and a suitable conventional fitting on the other end, such as a Luer lock adapter, or other means, for attaching a needle. A plunger or stem is reciprocable in the barrel and carries a piston on its inner end for developing vacuum or pressure, depending upon the direction of reciprocation of the piston and plunger in the barrel. A feature of the present invention is the use of the plunger, itself, as a guard for the needle after the syringe has been used. To this end, the plunger has a cavity formed in it, shaped to receive the needle and to remain securely attached to the syringe after it has been placed over the needle. In use, the plunger is simply removed from the barrel after the syringe has been used, and placed over the needle. There is no separate member which must be retrieved and used for this purpose.

Moreover, in a preferred embodiment, an entry slot is formed through the side of the plunger at the open end, through which the needle may be initially laterally placed prior to being axially fully inserted into the plunger, to thereby minimize the risk of pricking the finger of the person placing the guard over the needle.

Additionally, a small quantity of adhesive is positioned in the plunger/guard to permanently adhesively secure the plunger/guard to the needle after it is placed in operative position on the needle, thereby rendering the needle incapable of reuse.

In addition to tiie above features, the invention becomes inoperable after a single use, so that it cannot be used again. This is achieved by releasably attaching the piston to the end of the plunger by movable latch arms. The latch arms have over-center positions moving from latching engagement with latching fingers on the piston to an unlatched position freeing the latching fingers on the piston from the plunger. Thus, when the plunger and piston are reciprocated through one cycle rearwardly and then forwardly in the barrel, the latch arms move over-center out of engagement with the latching fingers, whereby a subsequent reciprocal movement of the plunger rearwardly in the barrel results in the piston becoming separated from the plunger so that it cannot be reattached to the plunger without the use of a special tool used during its manufacture, thus rendering the syringe incapable of further use.

Further, the piston of the invention is preferably made of a synthetic plastic material, resulting in a much less costly structure than conventional syringes in which the piston is typically made of a rubber material. To prevent set or "cold creep" of the seals of the plastic piston, a relief area is formed in the inner surface of the syringe barrel in the position occupied by the piston when it is in its at-rest, stored position fully inserted into the syringe barrel.

The piston also has a thin end wall that is easily pierced, so that a thin implement cannot be inserted through the forward end of the barrel in an effort to push the piston rearwardly in the barrel.

Brief Description of the Drawings:

The foregoing and other goals and advantages of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughout the several views, and wherein:

Fig. 1 is a perspective view of a hypodermic syringe incorporating the features of the invention.

Fig. 2 is a longitudinal view with parts shown in section of the syringe of figure 1 . Fig. 3 is a top plan view of the syringe, looking down on the top of figure 2.

Fig. 4 is an exploded perspective view of the syringe of figure 1 , with parts broken away and parts shown in section.

Fig. 5 is an enlarged, fragmentary, longitudinal sectional view of the end of the forward end of the syringe of the invention.

Fig. 6 is an enlarged fragmentary view of the end of the plunger in one form of the invention, as used in figures 1 -5.

Fig. 7 is a transverse sectional view taken along line 7-7 in figure 6.

Fig. 8 is a greatly enlarged fragmentary view in section of one of the latching arms carried by the end of the plunger, and showing its relationship with the wall of the barrel, the dot-and-dash lines representing the latched and unlatched over-center positions, respectively.

Fig. 9 is an enlarged fragmentary perspective view of one of the latching arms.

Fig. 10 is an enlarged, fragmentary, partly sectional view of the end of a modified plunger according to the invention.

Fig. 1 1 is an enlarged, fragmentary, longitudinal sectional view of the syringe of figure 1 , shown in its at-rest position with the piston latched to the plunger.

Fig. 1 2 is a fragmentary, longitudinal sectional view of the syringe of figure 1 1 , showing the plunger and piston being initially withdrawn in the barrel. Fig. 13 is an enlarged, fragmentary, longitudinal sectional view of the syringe of figure 1 1 , showing the plunger and piston being moved forwardly in the barrel, and depicting how the latching arms move rearwardly through their over-center position to release the latching fingers on the piston.

Fig. 14 is an enlarged, fragmentary, longitudinal sectional view of the syringe of figure 1 , shown with the piston seated at the bottom of the barrel following an injection, and with the plunger being withdrawn, with the piston unlatched from the plunger and remaining in the bottom of the barrel.

Fig. 1 5 is a fragmentary exploded view of the syringe of the invention, showing how the plunger may be used a needle guard upon its removal from the barrel.

Fig. 16 is a fragmentary view in elevation showing the plunger engaged on the Luer lock adapter of the syringe and secured in place as a needle guard for the needle.

Fig. 1 7 is a fragmentary, longitudinal sectional view of the plunger, showing the ampule of adhesive disposed in the plunger.

Fig 18 is a view similar to figure 1 7, showing how the adhesive in the ampule engages with the needle and with the plunger to fix the plunger to the needle.

Fig. 1 9 is a transverse sectional view taken along line 1 9-19 in figure

1 8.

Fig. 20 is a fragmentary, perspective sectional view of a portion of the bottom of the barrel and the piston, showing the thin piston end wall and the score lines therein which define weakened areas. Fig. 21 is a fragmentary perspective view of the end wall of the piston, showing how the end wall is pierced with an implement used in an attempt to push the piston rearwardly in the barrel.

Fig. 22 is an enlarged, fragmentary perspective view, with portions broken away and portions shown in section, of another form of the invention, wherein the latching arms are located in positions disposed 90° out of alignment with the body of the plunger; and

Fig. 23 is an exploded perspective view of the structure shown in figure 22, with the plunger unlatched from the piston.

Best Mode for Carrying Out the Invention:

Referring more specifically to the drawings, a syringe in accordance with the invention is indicated generally at 10 in figures 1 -9 and 1 1 -14. In this form of the invention, a cylindrical syringe barrel 1 1 has a forward end 12 with a suitable means, such as a Luer lock adapter 13, for attachment of a needle 14, and an open rearward end 15. A plunger 16 is reciprocable in the barrel, and carries a piston 17 at its forward end for drawing material into the plunger and discharging it through the needle.

The piston 17 is releasably connected to the plunger so that it is rendered inoperable after a single use. To this end, the piston has a plurality of rearwardly projecting latch fingers 18 that are molded with a radially outwardly oriented bias, so that they assume the position shown in figures 1 3 and 14 when they are unrestrained. In a preferred embodiment, there are six latch fingers spaced uniformly around the circumference of the piston.

The free end of each latch finger has a radially inwardly directed detent 19 that is adapted to engage behind a retaining ring 20 on the forward end of the plunger to hold the piston to the plunger when the latch fingers are urged inwardly to the position shown in figures 1 -5, 1 1 and 12. The latch fingers are held in this position by latching arms 21 and 22 carried on the plunger and engaged in encircling relationship over the free outer ends of at least some of the latch fingers. The piston 17 may be made of any suitable material, but in the form shown is made of plastic, and has two oppositely oriented, outwardly flared sealing rings 22 and 23 for sliding engagement against the inner surface of the syringe barrel. The inner surface of the barrel adjacent the end 12 is slightly diametrically enlarged at 25 to provide a relief area for seal 24 on the piston 17 when it is inserted fully into the barrel. This relief area prevents set of the piston seal 24 which might otherwise occur when the piston is made of plastic material and is stored in this position. The plunger 16 is reciprocable in the barrel between a forward position inserted fully into the barrel, and a rearward position retracted or withdrawn in the barrel, and has a forward end 26 that telescopically engages with a central bore 27 in the rearward side of the piston 17.

The rearward end 28 of the plunger has a radially enlarged operating flange 29 which may be gripped with the fingers and used to reciprocate the plunger in the barrel. This enlarged flange also forms a shield to protect the fingers when the plunger is being placed over a needle to serve as a needle guard.

The plunger may have a generally H-shaped transverse cross-section, with a central body 30 and oppositely extending flanges 31 and 32 along diametrically opposite sides of the body, with arcuate flanges 33 and 34 at their outer edges to slidably support the plunger in the barrel.

The plunger body 30 has a hollow, stepped configuration, including a larger tapered entry portion 30a adapted to receive the tapered portion 13 of the Luer adapter on the syringe barrel, an intermediate cylindrical portion 30b adapted to lock onto the cylindrical portion of the Luer lock fitting of the syringe barrel, and a reduced diameter tapered portion 30c adapted to closely receive the needle 14.

After the syringe 10 has been used, it is a simple matter for the doctor, nurse or other medical personnel to simply withdraw the plunger 16 from the barrel 1 1 and place the plunger over the needle, with the portions 30a and

30b locking onto the Luer lock adapter 13 of the syringe barrel, as shown in figures 1 5 and 1 6. There is no need for the doctor, nurse or other person using the syringe to search for and retrieve a separate needle guard, as is presently necessary in the prior art.

To facilitate placement of the plunger over the needle and to reduce the danger of accidentally pricking oneself with the needle while accomplishing this, an elongate slot 40 is formed through the side of the plunger body, leading from the end 28 and terminating at the end of the tapered portion 30a. Thus, the needle may be laid sideways into the slot and then slid lengthwise to fully seat the needle in the plunger/guard. This eliminates the danger of missing the relatively small opening in the end of the plunger when attempting to insert the needle lengthwise into the guard.

A small envelope 50 containing an adhesive 51 is located in the hollow bore portion 30c of the plunger in a position to be pierced by the needle 14 as the plunger is placed over the needle. The envelope 50 is roughly the size of a BB and is located at a point in the bore where small openings 52 and 53 are formed during the molding process. When the needle pierces the envelope, the adhesive 51 escapes and flows into the space surrounding the needle and into the two small openings 52 and 53, thereby forming a mechanical lock between the needle and the plunger and preventing removal of the plunger after the adhesive has cured . It should also be noted that it is anticipated that a small quantity of the adhesive will enter the end of the needle as it passes through the envelope of adhesive, plugging the needle and preventing its use even if access to it should be gained.

The releasable latching mechanism for releasably holding the piston to the plunger will now be further described. In addition to the retaining ring 20, latching arms 21 and 22, and the latching fingers 18, previously described, the latching mechanism includes an elongate bifurcated end 70 projecting beyond the retaining ring 20. The bifurcated end defines two semi-cylindrical posts 71 and 72 which extend into the bore 27 in the piston. The end of the plunger extending above the retaining ring 20 is hollow and is reinforced by a plurality of radially extending webs 73 which prevent inward flexing of the plunger end in the area of the retaining ring 20. See figure 7.

As seen in figure 1 1 , the ends of posts 71 and 72 are spaced from the end wall of the piston when the latching arms and latching fingers are operatively engaged behind the retaining ring 20. However, when the plunger is moved forwardly again after being retracted, as shown in figure 13, the latching arms 21 and 22 move to their over-center position due to frictional drag on the inner surface of the wall of barrel 1 1 , thereby releasing the latching fingers 18 and enabling them to spring outwardly, bringing the detents 19 out of registry with the retaining ring 20. Continued forward movement of the plunger causes the posts 71 and 72 to engage the end of the piston 17 to move it downwardly in the barrel 1 1 .

When the plunger is subsequently withdrawn, following ejection of a material from the syringe, as shown in figure 14, the posts 71 and 72 simply withdraw from the bore 27, leaving the piston seated at the bottom end of the barrel.

As seen best in figures 8 and 9, each latching arm (only latching arm 22 is shown and described here, it being understood that the latching arms 21 and 22 are identical) is joined to the plunger body by a relatively thin hinge area 74 to enable the arm to be easily flexed about the hinge. The outer ends of the arms are thickened in an axial direction relative to the longitudinal axis of the plunger, defining a radially inwardly facing shoulder 75 which engages against the outer surfaces of the arms 18 at their upper ends to hold the detents 19 in an inward position latched behind the retaining ring 20 on the plunger. See figures 1 1 and 12. A relatively narrow axially extending band 76 extends around the outer circumference of the arm for sliding engagement with the inner surface of the wall of barrel 1 1 . Inwardly tapered or sloping surfaces 77 and 78 extend upwardly and downwardly, respectively, from the band 76 to the top and bottom surfaces, respectively, of the arm. At approximately the mid-portion of the outer circumference of each arm, a rectangularly shaped enlargement or friction pad 79 extends downwardly from the band 76 to a point spaced just above the bottom surface of the arm. This area extends parallel and co-planer with the band 76 and defines a sliding surface against the inner surface of barrel wall 1 1 . As shown in figure 8, the arm is slightly longer than the radius of the inner surface of the wall of barrel 1 1 , whereby when the arm is in its horizontal position shown in figure 8 there is considerable frictional engagement between the band 76 and surface 79 with the inner surface of the barrel. Thus, when the plunger is withdrawn in the barrel, the arm slides along the inner surface of the barrel, but when the plunger is moved forwardly, the frictional drag between the band 76 and surface 79 with the inner surface of the barrel causes the arm to move rearwardly through an arc to an over-center position indicated by the dot and dash line OC in figure 8. The arms are also shown in this position in figures 13 and 14, and cannot be returned to their original position shown in full lines in figure 8 without use of a special tool to push the arms downwardly to engage against the outer surfaces of latching fingers 18 and hold the detents 19 behind the retaining ring 20. As seen best in figures 5, 1 1 -14, 20 and 21 , the end wall 80 of the piston is relatively thin, defining a membrane that may be relatively easily pierced. Accordingly, if an attempt should be made to insert a thin object such as a paper clip or the like through the Luer lock adapter end of the barrel to engage the piston and force it rearwardly in the barrel, the object will penetrate the wall 80 and render the piston useless. If desired, the wall 80 may be scored as indicated at 81 in figures 20 and 21 . Accordingly, when an implement such as a paper clip or the like C is inserted through the end 13 of the barrel 1 1 , the clip will penetrate the wall 80, causing it to fail along the score lines 81 and fold backwardly in a petal-like action, effectively destroying the end wall of the piston and rendering it impossible to use for drawing Iiquid into or expelling it from the syringe.

A modified plunger construction is indicated generally at 17' in figure 10. In this form of the invention, the Iower tapered body portion 30c' of the plunger is hollowed out all the way to the level of the retaining ring 20, as shown at 90, for receipt of a longer needle. In this form of the invention the Iower end of the plunger extending below the retaining ring 20 is shaped with a plurality of mutually orthogonally disposed flanges or webs 91 for extending into the bore 27 in the piston. In all other respects, this form of the invention functions identically to that previously described. A further form of the invention is indicated generally at 100 in figures

22 and 23. This form of the invention is essentially identical to that described in relation to figures 1 -6, except that the latching arms 21 ' and 22' are oriented in a position rotated 90° out of alignment with the semi-cylindrical flanges 33 and 34 on the plunger 16. To assemble the plunger to the piston, a special tool (not shown) having elongate pins is inserted through openings 101 and 102 in the flange 29 and extended downwardly past the body 33, 34 of the plunger to contact the upper surface of the latching arms 21 and 22 near their outer peripheries to force them downwardly about the hinges 74 and into latching engagement with the outer surfaces of the arms 18. In that form of the invention shown in figures 22 and 23, the arms 21 ' and 22' are offset circumferentially 90° out of alignment with the body 33, 34 of the plunger. An opening 105 is necessary in the flange 29' at the upper end of the plunger to gain access of the tool into that side. The other side is open by virtue of the slot 40, previously described.

It will also be noted that the openings 101 and 102 and the opening 105 through the respective collars 29 and 29'are provided with a small projection 106 that extends into the opening to prevent insertion of an implement other than the special tool which is designed for the purpose.

During assembly of the syringe of the invention, the piston is first inserted into the barrel through the open rearward end thereof, and the plunger is next inserted to bring the post and latching arms into juxtaposition with the piston. A special tool (not shown) is then inserted through the open end of the barrel and into contact with the latching arms, and is used to force the latching arms through their over-center position into the latched position shown in figure 5.

While the piston has been described herein as made of plastic, it should be understood that it may equally as well be made of rubber, as described in applicant's prior U.S. patent 5, 181 ,912. In such event, the piston itself may be constructed differently in the area where it seals with the barrel, but the latching mechanism is substantially identical to that previously described, and the hollow body for encasing the needle is the same as before.

The syringe of the invention is simple and economical in construction, and yet it provides an entirely different structure and function as compared with a conventional syringe, i.e., the plunger doubles as a needle guard after the syringe has been used, and the piston is connected to the plunger through a latched construction that automatically disables the syringe after a single use. The piston further incorporates structure that renders it unusable if an implement is used in an attempt to push the piston rearwardly in the barrel. While the invention has been illustrated and described in detail herein, it is to be understood that various modifications may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims.

What is claimed is:

Claims

C L A I M S

1 . A self-destructing non-reusable syringe, comprising: an elongate cylindrical barrel having adapter means on one end for attachment of a needle, and an open other end; an elongate plunger reciprocable in the barrel between a forward position in the barrel and a retracted position, said plunger having a forward end in the barrel and a rearward end accessible exteriorly of the barrel for operating the plunger; a piston releasably carried on the forward end of the plunger for effecting a sliding seal with the barrel to draw material into the barrel and discharge it therefrom through said one end upon reciprocating motion of the plunger and piston in the barrel, said piston being detachably connected to the plunger by releasable latch means that automatically disengages when the piston and plunger are reciprocated through one complete cycle of operation rearwardly and forwardly in the barrel; said releasable latch means comprising pivotable latch arms carried by the plunger and having a first pivoted latching position for latching engagement with pivotable latch fingers carried by the piston to hold the latch fingers inwardly against a retaining ring on the plunger to thereby hold the piston to the plunger, and a second pivoted unlatched position out of engagement with the latch fingers to release the fingers from the retaining ring and thereby release the piston from the plunger; and said plunger having access opening means for receipt of a tool inserted therethrough to engage the latch arms and move them into their first pivoted latching position to latch the piston to the plunger during assembly of the syringe.

2. A syringe as claimed in claim 1 , wherein: said plunger has a hollow bore formed longitudinally through a central portion thereof, said bore including a first portion for cooperative locking engagement with the adapter means on the barrel and a second portion for receipt of the needle, whereby the plunger may be withdrawn from the barrel and placed in shielding relationship over the needle after the syringe has been used for its intended purpose.

3. A syringe as claimed in claim 2, wherein: said piunger has an elongate slot formed in a side wall thereof, communicating with said bore and extending from said plunger open end toward the forward end, so that the plunger may be initially positioned laterally over said needle and then moved axially with respect thereto to fully seat the needle in the plunger.

4. A syringe as claimed in claim 3, wherein: the bore is formed in the plunger from the rearward end thereof, and terminates in a distal, closed end of the second portion.

5. A syringe as claimed in claim 4, wherein: a quantity of adhesive is contained within the bore in a position to be pierced by the needle when the plunger is placed over the needle, said adhesive serving to fix said plunger on said barrel in shielding relationship to said needle.

6. A syringe as claimed in claim 1 , wherein: the piston is made of plastic and has outwardly biased yieldable seals thereon for sealing, sliding engagement with an inner surface of the syringe barrel; and the syringe barrel has an enlarged diameter inner surface portion at its forward end, defining a relief area for the piston when it is in a stored position to prevent set or creep of the seals, whereby an effective seal is maintained between the piston and barrel.

7. A syringe as claimed in claim 6, wherein: the piston has a thin, membrane-like end wall on its forward end which is frangible if engaged with a thin implement inserted through the forward end of the barrel in an effort to push the piston rearwardly in the barrel after it has become disconnected from the plunger, thereby rendering the piston unusable.

8. A syringe as claimed in claim 1 , wherein: there are a plurality of latch arms pivotally joined to the forward end of the plunger, said latch arms having a circumferential extent adequate to encompass a plurality of the latch fingers on the piston to thereby securely attached the piston to the plunger; and each latch arm has an inner end pivotally connected to the forward end of the plunger, and an outer circumferentially extending end arranged for slidable movement along an inner surface of the barrel, said outer end having a thicker dimension than the inner end in an axial direction relative to the plunger and defining a radially inwardly facing shoulder which engages an outer upper end surface of the latch fingers carried by the piston.

9. A syringe as claimed in claim 8, wherein: the outer end of each latch arm includes an upper circumferentially extending tapered surface and a Iower circumferentially extending tapered surface, joined at their adjacent edges by a narrow circumferentially extending axially oriented band which slidably engages the inner wall of the barrel when the arm is in its normal latched position; and a small friction pad extends from the axially oriented circumferential band for sliding contact with the barrel inner surface to facilitate latching engagement of the latch arm during assembly of the syringe and prevent premature pivoted movement of the latch arm to its unlatched position as the plunger is reciprocated in the barrel.

10. A syringe as claimed in claim 9, wherein: the retaining ring is disposed further toward the forward end of the plunger than the point of pivotal attachment of the latch arms thereto, and the forward end of the plunger projects beyond the retaining ring and is bifurcated, defining a pair of forward projecting posts; and said piston has a bore formed in a rearwardly facing surface thereof for receipt of the forwardly projecting posts on the plunger, said posts serving to engage an end wall of the piston to push it forwardly in the barrel when the plunger is moved forwardly in the barrel.

1 1 . A self-destructing non-reusable syringe, comprising: an elongate cylindrical barrel having adapter means on one end for attachment of a needle, and an open other end; an elongate plunger reciprocable in the barrel between a forward position in the barrel and a retracted position, said plunger having a forward end in the barrel and a rearward end accessible exteriorly of the barrel for operating the plunger; a piston releasably carried on the forward end of the plunger for effecting a sliding seal with the barrel to draw material into the barrel and discharge it therefrom through said one end upon reciprocating motion of the plunger and piston in the barrel, said piston being detachably connected to the plunger by releasable latch means that automatically disengages when the piston and plunger are reciprocated through one complete cycle of operation rearwardly and forwardly in the barrel; said releasable latch means comprising a plurality of pivotable latch arms carried by the plunger and having a first pivoted latching position for latching engagement with pivotable latch fingers carried by the piston to hold the latch fingers inwardly against a retaining ring on the plunger to thereby hold the piston to the plunger, and a second pivoted unlatched position out of engagement with the latch fingers to release the fingers from the retaining ring and thereby release the piston from the plunger, said latch arms having a circumferential extent adequate to encompass a plurality of the latch fingers on the piston to securely attach the piston to the plunger, each latch arm having an inner end pivotally connected to the forward end of the plunger, and an outer end having a thicker dimension than the inner end in an axial direction relative to the plunger and defining a radially inwardly facing shoulder which engages an outer upper end surface of the latch fingers carried by the piston, the outer end of each latch arm including an upper circumferentially extending tapered surface and a Iower circumferentially extending tapered surface, joined at their adjacent edges by a narrow circumferentially extending axially oriented band which slidably engages the inner wall of the barrel when the arm is in its normal latched position, and a small friction pad extending from the axially oriented circumferential band for sliding contact with the barrel inner surface to facilitate latching engagement of the latch arm during assembly of the syringe and prevent premature pivoted movement of the latch arm to its unlatched position as the plunger is reciprocated in the barrel, said retaining ring being disposed further toward the forward end of the plunger than the point of pivotal attachment of the latch arms thereto, and the forward end of the plunger projecting beyond the retaining ring and being bifurcated, defining a pair of forward projecting posts; and said piston has a bore formed in a rearwardly facing surface thereof for receipt of the forwardly projecting posts on the plunger, said posts serving to engage an end wall of the piston to push it forwardly in the barrel when the plunger is moved forwardly in the barrel.

1 2. A syringe as claimed in claim 1 1 , wherein: the piston is made of plastic and has outwardly biased yieldable seals thereon for sealing, sliding engagement with an inner surface of the syringe barrel; and the syringe barrel has an enlarged diameter inner surface portion at its forward end, defining a relief area for the piston when it is in a stored position to prevent set or creep of the seals, whereby an effective seal is maintained between the piston and barrel.

13. A syringe as claimed in claim 12, wherein: the piston has a thin, membrane-like end wall on its forward end which is frangible if engaged with a thin implement inserted through the forward end of the barrel in an effort to push the piston rearwardly in the barrel after it has become disconnected from the plunger, thereby rendering the piston unusable.

14. A syringe as claimed in claim 1 2, wherein: said plunger has a hollow bore formed longitudinally through a central portion thereof, said bore including a first portion for cooperative locking engagement with the adapter means on the barrel and a second portion for receipt of the needle, whereby the plunger may be withdrawn from the barrel and placed in shielding relationship over the needle after the syringe has been used for its intended purpose.

1 5. A syringe as claimed in claim 14, wherein: said plungei has an elongate slot formed in a side wall thereof, communicating with said bore and extending from said plunger open end toward the forward end, so that the plunger may be initially positioned laterally over said needle and then moved axially with respect thereto to fully seat the needle in the plunger.

16. A syringe as claimed in claim 1 5, wherein: a diametrically enlarged circular flange is provided on the rearward end of the plunger to provide a shield for protecting the fingers from being pricked with a needle when the plunger is removed from the barrel and placed over the needle to serve as a needle guard.

1 7. A syringe as claimed in claim 1 1 , wherein: a diametrically enlarged circular flange is provided on the rearward end of the plunger to provide a shield for protecting the fingers from being pricked with a needle when the plunger is removed from the barrel and placed over the needle to serve as a needle guard.

18. A self-destructing non-reusable syringe, comprising: an elongate cylindrical barrel having adapter means on one end for attachment of a needle, and an open other end; an elongate plunger reciprocable in the barrel between a forward position in the barrel and a retracted position, said plunger having a forward end in the barrel and a rearward end accessible exteriorly of the barrel for operating the plunger; a piston releasably carried on the forward end of the plunger for effecting a sliding seal with the barrel to draw material into the barrel and discharge it therefrom through said one end upon reciprocating motion of the plunger and piston in the barrel, said piston being detachably connected to the plunger by releasable latch means that automatically disengages when the piston and plunger are reciprocated through one complete cycle of operation rearwardly and forwardly in the barrel; and said piston is made of a synthetic plastic material and has outwardly biased yieldable seals for sealing, sliding engagement with an inner surface of the syringe barrel, and has a thin forward end wall which is frangible if an implement is inserted through the forward end' of the barrel and engaged against the piston end wall in an effort to push the piston rearwardly in the barrel after it has become disengaged from the plunger.

19. A syringe as claimed in claim 18, wherein: said releasable latch means comprises pivotable latch arms carried by the plunger and having a first pivoted latching position for latching engagement with pivotable latch fingers carried by the piston to hold the latch fingers inwardly against a retaining ring on the plunger to thereby hold the piston to the plunger, and a second pivoted unlatched position out of engagement with the latch fingers to release the fingers from the retaining ring and thereby release the piston from the plunger.

20. A syringe as claimed in claim 1 9, wherein: there are a plurality of latch arms pivotally joined to the forward end of the plunger, said latch arms having a circumferential extent adequate to encompass a plurality of the latch fingers on the piston to thereby securely attach the piston to the plunger, each latch arm having an inner end pivotally connected to the forward end of the plunger, and an outer circumferentially extending end arranged for slidable movement along an inner surface of the barrel, said outer end having a thicker dimension than the inner end in an axial direction relative to the plunger and defining a radially inwardly facing shoulder which engages an outer upper end surface of the latch fingers carried by the piston, the outer end of each latch arm including an upper circumferentially extending tapered surface and a Iower circumferentially extending tapered surface, joined at their adjacent edges by a narrow circumferentially extending axially oriented band which slidably engages the inner wall of the barrel when the arm is in its normal latched position, and a small friction pad extends from the axially oriented circumferential band for sliding contact with the barrel inner surface to facilitate latching engagement of the latch arm during assembly of the syringe and prevent premature pivoted movement of the latch arm to its unlatched position as the plunger is reciprocated in the barrel; said retaining ring being disposed further toward the forward end of the plunger than the point of pivotal attachment of the latch arms thereto, and the forward end of the plunger projecting beyond the retaining ring and being bifurcated, defining a pair of forward projecting posts; and said piston has a bore formed in a rearwardly facing surface thereof for receipt of the forwardly projecting posts on the plunger, said posts serving to engage an end wall of the piston to push it forwardly in the barrel when the plunger is moved forwardly in the barrel.

21 . A syringe as claimed in claim 20, wherein: said plunger has access opening means for receipt of a tool inserted therethrough to engage the latch arms and move them into their first pivoted latching position to latch the piston to the plunger during assembly of the syringe.

22. A syringe as claimed in claim 18, wherein: the thin forward end wall of the piston is flat, and an inner surface of the forward end of the barrel is flat to form a surface complemental to the flat end wall of the piston, whereby when the plunger and piston are moved fully forwardly in the barrel substantially all material can be ejected from the barrel.

23. A syringe as claimed in claim 18, wherein: the piston end wall is scored to define weakened areas which cause the wall to fracture or tear when it is pierced.