Abstract:
A syringe ( 1 ) comprises a barrel ( 2 ) having a needle ( 23 ) engaged in a glass hub ( 19 ). The glass hub ( 19 ) is retractable under the action of a spring ( 30 ) towards the trailing end of the syringe. The glass hub ( 19 ) is restrained against movement towards the trailing end by a crown ( 10 ) which is removably attached to the glass hub ( 19 ). A plunger ( 36 ) engages the crown ( 10 ), removing it from the glass hub ( 19 ) and allowing retraction of the needle ( 23 ). A core ( 45 ), removably attached to the end of the plunger by a resiliently deformable member, is then removed from the plunger, allowing the glass hub ( 19 ) and the needle ( 23 ) to be retracted into the plunger under the action of the spring ( 30 ).

Description:
FIELD OF THE INVENTION  
       [0001]     The present relates to a syringe and, in particular, a syringe having a retractable needle. The present invention also relates to a collar attachable to a syringe and a needle unit for a syringe.  
       DESCRIPTION OF THE PRIOR ART  
       [0002]     It has long been known to administer medicaments and the like transcutaneously to an individual by using a syringe having a hypodermic needle. The syringe has a plunger slidably received in a barrel and, when the plunger is depressed, a liquid medicament is expelled from the hypodermic needle.  
         [0003]     The problem with such syringes is that the hypodermic needle remains an extremely sharp object after use which can be dangerous both because of the physical damage that such a sharp object can cause and because, once the needle has been inserted into an individual, it may transmit infections that the individual was carrying.  
         [0004]     One solution to this problem is to place a cap, or sheath, over the needle after it has been used so that the needle is enclosed. However, the problem with doing this is that, in practice, it is quite difficult to place such a cap over the end of the syringe. The needle is very thin and an individual may accidentally prick himself with the needle when attempting to put the cap in place. Furthermore, the cap may inadvertently fall off the syringe, once it has been fitted.  
         [0005]     Another problem with this type of syringe is that, amongst certain groups of people (e.g. illegal drug users) there is a temptation to use syringes repeatedly, with the same needle, which results in a very high risk of cross-infection between members of the group.  
         [0006]     Accordingly, a solution to the problems encountered with such syringes is a syringe with a retractable needle. WO-A-96/05879 discloses such a syringe wherein the needle is spring-loaded so that, when the plunger in the syringe reaches the end of its stroke, a frangible section in a leading end of the plunger is broken off.  
         [0007]     Furthermore, a restraining member, which holds the needle in place, against the force of the spring is dislodged so that the spring forces the needle through the leading end of the plunger and into the hollow interior of the plunger. Thus, once all (or almost all) of the liquid has been expelled from the barrel of the syringe, the needle is automatically retracted into the interior of the plunger, which lies within the barrel of the syringe. Thus, once the needle has been retracted, it is no longer a danger to others and the syringe may not be reused.  
         [0008]     WO-A-02/087669 also discloses a syringe having a retractable needle. A hub, which is attached to the needle, and the restraining member are formed as plastic mouldings that engage with one another and which are disengaged at or towards the end of the plunger&#39;s stroke.  
         [0009]     Syringes are normally supplied empty, so that an individual may choose a particular medicament or the like to draw into the syringe before administering it. However, for the sake of convenience, it is also known to supply pre-filled syringes, especially of the most commonly required medicaments such as insulin.  
         [0010]     The problem that arises with pre-filled syringes is that, while normally the majority of the components of a syringe are made from plastics materials, this is not possible with pre-filled syringes because the syringes may be stored for relatively long periods of time in which the enclosed medicament is in contact with the plastics materials. Some medicaments are not stable when they are in long term contact with a plastics material and, in practice, it is often difficult to determine whether or not a particular medicament is stable when in contact with a particular plastics material (or, at least, it is difficult to obtain the appropriate medical authorisation to store the medicaments in a plastics material). Therefore, it is almost always necessary for the components of a pre-filled syringe that come into contact with the medicament to be made either from glass or from rubber but not from a plastics material. This presents a problem for producing a pre-filled syringe with a retractable needle because the syringes with retractable needles disclosed in the prior art (for example WO-A-96/05879 and WO-A-02/087669) rely on components which are made from a plastics material, in particular the frangible or disengagable components disclosed therein.  
         [0011]     Another problem with the syringes having retractable needle mechanisms known in the prior art is that the needle retraction mechanisms may inadvertently be activated prematurely. For example, during transport of the syringe, the plunger of the syringe may be depressed with sufficient force to activate the retraction mechanism. Of course, once the needle has been retracted, the syringe cannot be used and is wasted.  
         [0012]     Another problem that arises, generally, in the field of syringes is that, during use, the plunger is inadvertently drawn so far along the barrel of the syringe that it actually falls completely out of the end of the barrel. One instance where this can occur is when the syringe is being filled (although this will not, of course, occur if it is a pre-filled syringe). Another instance is while the medicament is administered to an individual. One technique for use of a syringe is, having inserted the hypodermic needle into a blood vessel of the individual, to draw a little blood from the individual by withdrawing the plunger slightly. This allows the individual performing the injection to be certain that the hypodermic needle has been inserted into a blood vessel. In either of these two instances, the plunger may, inadvertently, be withdrawn too far and, if so, the contents of the syringe is usually lost and the procedure must be repeated.  
         [0013]     It is known in the art to provide a stop at the end of the barrel of the syringe in order physically to prevent the plunger from being withdrawn too far. The problem, however, with pre-filled syringes is that, as has previously been explained, the barrel of the pre-filled syringe must be made from glass. There are limitations to the complexity that can be introduced into the shape of a glass barrel and therefore it is not usually possible for the glass barrel to have any form of stop to prevent the withdrawal of the plunger. Therefore, pre-filled syringes still suffer from the problem of the plunger being inadvertently withdrawn too far.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention seeks to alleviate one or more of the above problems.  
         [0015]     According to one aspect of the present invention, there is provided a syringe comprising: 
        a barrel having leading and trailing ends;     a hollow bore needle extending from the leading end of the barrel and carried by a needle hub;     a resilient member connected between the barrel and the needle hub so as to urge the needle hub and the needle toward the trailing end of the barrel;     a crown removably attached to the needle hub and the barrel and preventing movement of the needle hub under the influence of the resilient member; and     a plunger slidably moveable within the barrel; 
 
 wherein, when the plunger is moved along the barrel towards the leading end, the plunger engages the crown so as to release the attachment between the crown and the needle hub allowing the needle hub, and the needle to be retracted by the resilient member. 
       
 
         [0022]     Conveniently, the plunger carries a removable core at its leading end leading to a hollow interior, the hollow interior being sized to receive the needle and the needle hub such that, when the plunger is moved along the barrel towards the leading end, the needle hub engages the core so as to release the attachment between the core and the plunger allowing the needle hub, and the needle to be retracted into the hollow interior of the plunger by the resilient member.  
         [0023]     Preferably, the core is removably attached to the plunger via a resiliently deformable member.  
         [0024]     Advantageously, the crown is removably attached to the needle hub via a resiliently deformable member.  
         [0025]     Conveniently, the resiliently deformable member attaching the crown to the needle hub forms a seal around the crown, between the needle hub and the barrel.  
         [0026]     Preferably, the resiliently deformable member attaching the core to the plunger forms a seal around the end of the plunger, between the removable core and the barrel.  
         [0027]     Advantageously, the two resiliently deformable members are made from rubber and the barrel, the needle hub and the removable core are made from glass.  
         [0028]     According to another aspect of the present invention, there is provided a needle unit for a syringe, the needle unit comprising: 
        a needle connected to a retraction mechanism for retracting the needle; and     a removable sheath for enclosing the needle, 
 
 wherein the sheath engages the retraction mechanism when it encloses the needle to prevent retraction of the needle prior to removal of the sheath. 
       
 
         [0032]     According to a further aspect of the present invention, there is provided a syringe comprising such a needle unit.  
         [0033]     According to another aspect of the present invention, there is provided a collar for attachment to a syringe having a barrel and a retractable plunger extending from one end of the barrel the collar comprising: 
        means to grip said end of the barrel; and     at least one stop member located so that, when the collar is attached to the barrel, the stop member projects over said end of the barrel such that, when the plunger is retracted from the barrel, a portion of the plunger impinges on the stop, preventing removal of the plunger from the barrel.        
 
         [0036]     Conveniently, the collar is made from a plastics material.  
         [0037]     According to a further aspect of the present invention, there is provided a syringe comprising: a barrel; a retractable plunger extending from one end of the barrel; and a collar as described above.  
         [0038]     Preferably, the barrel is made from glass.  
         [0039]     Throughout this specification, it is to be understood that the term “leading end” refers to the end of the syringe, or a component of the syringe, towards the needle whereas the term “trailing end” refers to the end of the syringe, or a component of the syringe, towards the plunger. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]     In order that the present invention may be more readily understood, and so the further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:  
         [0041]      FIG. 1A  is an axial cross-sectional view of a syringe in accordance with an embodiment of the present invention;  
         [0042]      FIG. 1B  is an enlarged view of the leading end of the syringe shown in  FIG. 1A ;  
         [0043]      FIG. 1C  is an enlargement of the needle unit of the syringe shown in  FIG. 1A ;  
         [0044]      FIG. 1D  is an enlargement of a section of the plunger of the syringe shown in  FIG. 1A ;  
         [0045]      FIG. 1E  is an enlargement of the trailing end of the barrel of the syringe shown in  FIG. 1A ;  
         [0046]      FIG. 2  is a perspective view of a needle unit of a syringe in accordance with an embodiment of the present invention, with part cut away;  
         [0047]      FIG. 3  is a perspective view of a section of a plunger of a syringe in accordance with an embodiment of the present invention, with part cut away; and  
         [0048]      FIG. 4  is a perspective view of a section of the trailing end of a syringe in accordance with an embodiment of the present invention, with part cut away. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]     Referring to  FIG. 1  (and the enlargements  FIGS. 1B, 1C ,  1 D and  1 E), a syringe  1  is shown in axial cross-section. The syringe  1  comprises a hollow glass barrel  2  which is substantially cylindrical. At its leading end  3 , the barrel  2  narrows to a neck  4  in which is received a needle unit  5  which is held in place by a generally annular end cap  6 . The end cap  6  sits around the exterior of the neck  4  having an inwardly projecting ridge  7  which sits in an annular groove  8  in the exterior of the neck  4 . The end cap  6  is also provided with a leg  9  which protrudes over the leading end  3  of the barrel so that the end of the leg lies flush with the interior surface of the barrel  2 . Thus the end cap  6  holds the needle unit  5  in place as will be described in greater detail below.  
         [0050]     The needle unit  5 , which is shown in detail in  FIG. 1C , comprises a generally annular crown  10  made from a plastics material, which abuts the interior of the neck  4  of the barrel  2 . At its leading end, the crown  10  has a radially outwardly extending leg  11  which sits over the leg  9  of the end cap  6 . Thus the crown  10  is prevented from moving towards the trailing end of the barrel  2 . The end of cap  6  has four cut outs  31 , equally spaced about its circumference, which expose the leg  11  of the crown  10 . Towards the trailing end of the crown  10  is a step leading to a finger  12 . The finger  12  sits radially inwardly of the neck  4  of the barrel  2  and thus an annular channel  13  exists between the finger  12  and the neck  4 .  
         [0051]     Also comprised in the needle unit  5  is a generally annular needle unit seal  14  made from rubber. The needle unit seal  14  has a central section  15  which sits radially inwardly of the crown  10 . The central section is of the needle unit seal  14  and the adjacent section of the crown  10  are shaped so as to mutually engage one another about a ramped step  26  which is formed such that the needle unit seal  14  is thicker and the crown  10  is thinner in the leading direction from the ramped step  26 . Thus the engagement of the needle unit seal  14  and the crown  10  at the ramped step  26  prevents the movement of the crown in a leading direction and the movement of the needle unit seal  14  in a trailing direction.  
         [0052]     At its trailing end, the needle unit seal  14  has a U-shaped section  16  which extends in a trailing direction before extending around the finger  12  of the crown  10  and then extending inwardly to sit in the annular channel  13 . Thus, the U-shaped section  16  effectively encapsulates the trailing end of the crown  10 . At its leading end, the needle unit seal  14  has a radially inwardly extending ridge  17 , which will be described in greater detail below and, at its tip, a radially outwardly extending flange  18  which sits over the leg  11  of the crown  10 .  
         [0053]     The crown  10  and the needle unit seal  14  can be produced together by a two shot injection moulding process.  
         [0054]     Also forming part of the needle unit  5  and located radially inwardly of the needle unit seal  14  is a substantially cylindrical glass hub  19  which has an axial bore therethrough. The trailing end  20  of the glass hub  19  lies flush with the end of the U-shaped section  16  of the needle unit seal  14 . Around the exterior of the glass hub  19 , towards its leading end  21 , there is provided an annular groove  22 , in which the ridge  17  of the needle unit seal  14  is received. A hollow bore needle  23  extends through the axial bore of the glass hub  19  and is attached thereto.  
         [0055]     It is to be appreciated that the needle unit seal  14  provides a seal between the barrel  2  and the glass hub  19 , preventing the passage of liquid therebetween.  
         [0056]     Adjacent the leading end  21  of the glass hub  19  the end cap  6  forms a hollow, frustro-conical nose  24 . At the trailing end of the nose  24  is provided a narrow ring  25  which abuts the leading end  21  of the glass hub  19  and spaces the nose  24  from the flange  18  of the needle unit seal  14 , thus leaving an annular chamber  27  therebetween. There is an aperture  29  in the leading end  28  of the nose  24 . The needle  23  extends through the nose  24  and exits the nose  24  through the aperture  29 .  
         [0057]     Received within the hollow interior of the nose  24  is a coiled spring  30  which extends axially, around the needle  23 , from the leading end  21  of the glass hub  19  to the leading end  28  of the nose  24 . The spring  30  is under compression and therefore presses against the leading end  28  of the nose  24  to urge the hub  19  (together with the needle  23  which is attached thereto) in a trailing direction. However, the engagement of the ridge  17  of the needle unit seal  14  in the groove  22  of the hub  19  prevents the hub  19  from moving in a trailing direction. In this regard, it is to be appreciated that the needle unit seal  14  is prevented from moving in a trailing direction because of its engagement with the crown  10  and, in particular, the engagement of the flange  18  over the leg  11  of the crown  10 . It is also to be appreciated that the crown  10  is prevented from moving in a trailing direction because of the engagement of the leg  11  of the crown  10  over the leg  9  of the end cap  6 .  
         [0058]     Encasing the needle unit  5  of the syringe  1  is a cap, or sheath  32  which is removably seated around the end cap  6 , including the nose  24  thereof. The cap  32  has four radially inwardly extending ribs  33  which are equally spaced about the interior circumference thereof. The ribs  33  are received in the cut outs  31  of the end cap  6  and sit against the leading edge of the leg  11  of the crown  10 . Thus, while the cap  32  is in place, the ribs  33  prevent the movement of the crown  10  in a leading direction.  
         [0059]     A rubber bung  34  is provided in the inside of the tip of the cap  32  as is shown in  FIG. 1B . The tip of the needle  23  is removably received in the rubber bung  34 . The friction between the needle  23  and the rubber bung  34  prevents accidental removal of the cap  32 .  
         [0060]     Having thus described the needle unit  5  of the syringe  1 , the other components of the syringe  1  will now be described.  
         [0061]     Received in the trailing end  35  of the barrel  2  is a hollow plunger  36  whose exterior circumference is slightly smaller than the interior circumference of the barrel  2 . As is most clearly shown in  FIG. 1D , at the leading end of the plunger  36  a screw thread on the interior of the plunger  36  engages with an actuator element  37  which is generally tubular. The leading end of the actuator element  37  terminates in a narrow annular finger  38  whose outer circumference is less than the inner circumference of the barrel  2 . Thus an annular cavity  39  exists between the finger  38  and the interior of the barrel  2 . Sitting in the cavity  39  is a plunger seal  40  which is of approximately “J” shaped cross-section and is made from rubber. Thus the plunger seal  40  has a body  41  which sits in the annular cavity  39  between the barrel  2  and the narrow annular finger  38 . The body  41  leads to an end section  42  which sits over the leading end of the actuator element  37  and then leads to an inner section  43  on the inner surface of the actuator element  37 . Thus the plunger seal  40  encapsulates the end of the actuator element  37 . The inner section  43  of the plunger seal  40  has a radially inwardly projecting ridge  44  which will be described in further detail below.  
         [0062]     The actuator element  37  and the plunger seal  40  can be produced together by a two hot injection moulding process.  
         [0063]     Located within the hollow interior of the actuator element  37  is a substantially cylindrical glass core  45  having a diameter greater than the glass hub  19 . The glass core  45  is held in place within the actuator element  37  by the engagement of the inwardly projecting ridge  44  of the plunger seal  40  in an annular groove  46  located in the exterior of the glass core  45 , towards its leading end  47 . The leading end  47  of the glass core  45  is recessed slightly compared with the end section  42  of the plunger seal  40  which thus protrudes around the leading end  47  of the glass core  45 .  
         [0064]     The plunger seal  40  fits tightly against the interior of the barrel  2  and thus has a greater circumference than the plunger  36 . Accordingly, the plunger seal  40  provides a seal between the glass core  45  and the interior of the barrel  2 . Thus, while the plunger seal  40  allows the plunger  36  to be moved slidably within the barrel  2 , it also prevents the escape of a liquid, such as a medicament, contained within a storage chamber  48  which is defined by the barrel  2 , the plunger  36  and the needle unit  5 .  
         [0065]     As is shown in  FIG. 1E , at the trailing end  49  of the plunger  36  is provided a mushroom-shaped grip  50  having a circumference greater than the circumference of the barrel  2 .  
         [0066]     The trailing end of the barrel  2  has an enlarged radially outwardly projecting rim  51 . A plastic collar  52  is clipped onto the enlarged rim  51  by means of an annular claw  53 . The claw  53  comprises a leading leg  54  which sits on the leading side of the rim  51  and a trailing leg  55  which sits on the trailing side of the rim, at the very end of the trailing end of the barrel  2 . The trailing leg  55  extends radially inwardly, beyond the interior surface of the barrel  2 , but not so far as to contact the outer surface of the plunger  36 .  
         [0067]     The trailing end of the collar  52  comprises an annular wall  56  defining a cylindrical recess  57  which is sized to receive the plunger  36  and, more particularly, the grip  50 . The inner circumference of the annular wall  56  is only very slightly larger than the circumference of the mushroom-shaped grip  50  and thus is sized to receive the grip with a snug fit.  
         [0068]     In use, the syringe  1  is manufactured so as to have a liquid contained within the storage chamber  48 . The liquid is typically a medicament such as insulin. Thus the syringe  1  is a pre-filled syringe. It is to be appreciated that the components of the syringe  1  which are in contact with the liquid contained in the storage compartment (namely the barrel  2 , the needle unit seal  14 , the glass hub  19 , the plunger seal and the glass core  45 ) are all made from materials with which the liquid may safely come into contact without being degraded. Thus, the pre-filled syringe may be stored for long periods of time without the liquid being affected.  
         [0069]     Even though the barrel  2  is made from glass, the plastic collar  52  is still provided, clipped to the barrel  2 , in order to prevent over-withdrawal of the plunger  36  and re-use of the syringe  1  as is explained in greater detail below.  
         [0070]     In order that the storage chamber  48  is of suitable size so that a sufficient quantity of liquid is stored therein, the plunger  36  is in a withdrawn position, most of the way out of the barrel  2 . Thus the plunger  36  extends out of the end of the barrel  2  and the collar  52  and the grip  50  sits remote from the collar  52 .  
         [0071]     It is also to be noted that, when stored, the sheath or cap  32  is held in place by its frictional engagement with the end cap  6  and by the engagement of the needle  23  in the rubber bung  34 . While the cap  32  is held in this position, the rib inwardly extending ribs  33  on the cap  32  engage the crown  10  and prevent the movement of the crown  10  in a leading direction.  
         [0072]     When it is desired to administer the liquid contained in the syringe to an individual, the cap  32  is removed from the leading end of the syringe  1  by pulling the two components apart axially. As will be appreciated, once the cap  32  has been removed, the crown  10  is no longer prevented from moving towards the leading end of the syringe  1  by the inwardly extending ribs  33  on the cap  32  although it is still prevented from such movement by the engagement with the needle unit seal  14  at the ramped step  26  and the flange  18 .  
         [0073]     The needle  23  is then inserted into the blood vessel of the individual as is usual with hypodermic syringes. If desired, the plunger  36  may then be slid slightly outwardly of the barrel  2  by pulling on the grip  50 . In this way, a small amount of blood is drawn into the needle  23  and the storage chamber  48  which can be seen and which thus confirms that the needle  23  is, indeed, located in a blood vessel. During the process of sliding the plunger  36  outwardly of the barrel  2 , it is not possible for the plunger  36  to be completely removed from the barrel  2  because the trailing leg  55  of the claw  53  of the collar  52  projects over the trailing end of the barrel  2  and impinges upon the plunger seal  40  as the plunger  36  is drawn out of the barrel  2 . When the plunger seal  40  impinges upon the trailing leg  55 , further movement of the plunger  36  in a trailing direction is prevented.  
         [0074]     Whether or not there is any withdrawal of the plunger  36 , the next step in administering the liquid is for the plunger  36  to be slid along the barrel  2  towards the leading end of the barrel  2 . This is achieved by depressing the grip  50 . The liquid in the chamber  48  is thus pressurised and, when sufficient pressure is reached, the liquid is expelled via the needle  23  out of its tip and into the blood vessel of the individual, as is normal for hypodermic syringes known in the art.  
         [0075]     As the plunger  36  continues to be depressed, the leading end  42  of the plunger seal  40  comes into contact with the trailing end  16  of the needle unit seal  14 . It is to be noted that the leading end  42  of the second rubber seal  40  is similarly sized and aligned with the trailing U-shaped section  16  of the needle unit seal  14 . Thus, when the respective seals  14 ,  40  meet, the user of the syringe  1  can feel an appreciable increase in the force required to depress the plunger  36 . However, if the user continues to depress the plunger  36 , then the plunger seal  40  pushes the needle unit seal  14  towards the leading end of the syringe  1  with the inwardly extending ridge  17  of the needle unit seal  14  being radially outwardly compressed and deflected by virtue of its resilient nature, and thus pushed out of the annular groove  22  in the glass hub  19 . Because of the engagement of the needle unit seal  14  about the finger  12  of the crown  10 , the crown  10  is also pushed in a leading direction. Thus the flange  18  of the needle unit  14  is pushed into the annular chamber  27  as the needle unit seal  14  slides axially against the glass hub  19  and the crown  10  slides axially against the neck  4  of the barrel  2 .  
         [0076]     It is to be appreciated that, as the ridge  17  of the needle unit seal  14  leaves the groove  22  in the glass hub  19 , the urging of the glass hub  19 , towards the trailing end of the syringe  1 , by the spring  30  is no longer restrained by the crown  10  and the needle unit seal  14 .  
         [0077]     However, as has previously been explained, the leading end  47  of the glass core  45  is recessed compared with the plunger seal  40 . As the plunger seal  40  pushes the needle unit seal  14  towards the leading end of the syringe  1 , the leading end  47  of the glass core  45  comes into contact with the trailing end  20  of the glass hub  19 . Accordingly, the glass core  45  prevents the movement of the glass hub  19  towards the trailing end of the syringe  1  under the action of the spring  30 .  
         [0078]     As the user of the syringe  1  continues to depress the plunger  36 , the leading end  47  of the glass core  45  presses against the trailing end  20  of the glass hub  19 . The glass hub  19  is effectively prevented from moving towards the leading end of the syringe  1  because it rests against the ring  25  of the end cap  6  which is firmly attached to the neck  4  of the barrel  2 . Thus a force is applied to the glass core  45  in a trailing direction. Once a predetermined threshold of force has been reached, the inwardly projecting ridge  44  of the plunger seal  40  is radially outwardly compressed and deflected by virtue of the resilient nature of the ridge  44 , and pushed out of the groove  46  in the glass core  45 . Once the ridge  44  of the plunger seal  40  has been pushed out of the groove  46  in the glass core  45 , the spring  30  is able to act to urge the glass hub  19 , the needle  23 , to which it is attached, and the glass core  45  towards the trailing end of the syringe  1  which is thus enclosed in the hollow interior of the plunger  36 . It is to be noted that since the glass hub  19  is of slightly smaller diameter than the glass core  45 , the glass hub  19  does not impinge upon the ridge  44  of the plunger seal  40 . Accordingly, the needle  23  is retracted inwardly and is encased within the barrel  2  and the plunger  36  once the plunger is fully depressed so that the syringe  1  cannot be reused and, furthermore, the needle  23  is safely enclosed within the syringe  1 . Thus the needle  23  is no longer a scratch or puncture hazard.  
         [0079]     As the plunger  36  is depressed, the grip  50  is received within the cylindrical recess  57  of the collar  52 . The wall  56  which thus surrounds the grip  50  is relatively tight fitting. The fit is such that the grip  50  may readily continue to be depressed but it is very difficult, if not impossible, for the grip  50  to be pulled outwardly since there is no surface on which a user may get a purchase on the grip  50 . Thus, the user (or, indeed, any other individual) is prevented from retracting the plunger  36 , once the grip  50  has passed the end of the wall  56 . Consequently, it is not possible for the plunger  36  to be retracted and the syringe reused.  
         [0080]     In  FIGS. 2, 3  and  4 , portions of a further embodiment of the present invention are shown. The further embodiment is only very slightly different from the above described embodiment and the corresponding components are given the same reference numbers. The functioning of the further embodiment is substantially the same as the above described embodiment.