US3403680A - Hypodermic injection apparatus - Google Patents

Description

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United States Patent O 3,403,680 HYPODERMIC INJECTIN APPARATUS Kenneth Sinclair, Winterslow, and Cyril Dani Watson, Idmiston, England, assignors to The Secretary of State for Defence in Her Britannie Majestys Government of the United Kingdom of Great Britain and Northern Ireland, London, England Continuation-impart of application Ser. No. 512,884, Dec. 10, 1965. This application June 13, 1966, Ser. No. 557,219 Claims priority, application Great Britain, Dec. 11, 1964, 50,617/ 64 10 Claims. (Cl. 12S-218) ABSTRACT F THE DISCLOSURE A hypodermic syringe comprises a releasable main spring and a liquid-containing chamber with a puncturable forward end and a non-collapsible rear end portion. The rear end has a tubular well which opens into the chamber, with a deformable plunger located in the entrance to the well. The main spring drives the rear end, the deformable plunger and a hypodermic needle which is accommodated in the deformable plunger, into the flesh of the user. If the needle encounters resistance during its forward travel, the deformable plunger is displaced rearwardly into the tubular well so that the injection of the dose is completed.

This is a continuation-in-part of application Ser. No. 512,884 filed December l0, 1965.

The invention relates to hypodermic injection apparatus mainly for the self administration of therapeutic or prophylactic agents or for veterinary work. The invention relates more particularly to injection apparatus or syringes in which a hypodermic needle is housed within the appar-atus before an injection operation is performed and which are used for intra-muscular injections well into the flesh.

In some previously known hypodermic syringes a hypodermic needle is supported within a liquid-containing chamber which may be a tube or a sealed collapsible capsule located within the forward end of the casing of the syringe. The forward end of the chamber is punctur-able by the needle. In these hypodermic syringes a plunger is disposed within the casing at the rear end of the chamber which when released is driven forward by a spring to drive the point of the needle through the forward end of the chamber and into the skin of the user, and thereupon cause the injection of the liquid through the needle and into the flesh.

In these spring-loaded automatic hypodermic syringes the discharge of liquid from the needle must take place while the needle is actually penetrating into the flesh and the discharge is substantially completed by the time the needle has completed its course. Powerful actuating springs are employed in order to effect a rapid injection and minimise pain, and it has been found in practice that the discharge of liquid from these devices can be so impeded that a seriously incomplete dosage can often result when, as is usual and desirable, the injection is given into a muscle and the needle comes into unrelenting contact with the facia of gristle which is found between layers of muscle and is thereby blocked and the further discharge of liquid prevented.

The length of the needle must be just shorter than that of the chamber, so that when the plunger is released the forward end of the chamber is rapidly punctured and the liquid can be ejected through the needle without any risk of the chamber bursting or the device being prevented from oper-ating. The needle thus enters the flesh to a ice depth just less than the length of the needle and the liquidcontaining chamber and this depth of penetration may in various circumstances be greater than what is desirable or necessary, for example, if an injection were to be self l administered with known injectors of this type by a person suffering a partial mental or physical collapse or having thin muscles the needle could hit a bone, and since the needle is usually injected with high force and velocity by the spring serious bone damage could result. Furthermore, the obstruction of the needle by the bone can seriously reduce the amount of liquid which can be injected.

The object of the present invention is to reduce the frequency of these maloperations which could have serious or fatal consequences and provide a quick acting automatic self-injection hypodermic syringe which is as far as possible safe and painless to use even by unskilled users in a state of partial mental or physical collapse.

According to the present invention, a hypodermic syringe for making injections into the body of a user comprises releasable main spring means, a liquid-containing chamber with a puncturable forward end and a noncollapsible rear end portion adapted to be driven by the main spring means and having a tubular well which opens into the chamber, a deformable plunger located in the entrance to the well, and a hypodermic needle which priorto-use is disposed through almost the full length of the chamber with its point directed to the puncturable forward end and its head accommodated in the deformable plunger so that it can be driven forward when the main spring is released, the plunger being deformed and displaceable into the tubular well when the needle is subjected to a given resistance to its forward travel.

With hypodermic syringes in accordance with the invention having a deformable plunger arranged to operate when a resistive force is applied of between about 5 and 10 1b. it has been found possible to give afconsiderably higher proportion of satisfactory injections than before. The resistive force can be applied when the needle is driven into either a gristle facia or a bone. Thus while the chamber is still contracting in volume to eject liquid from the needle the plungercan be deformed by the applied force and slide back into the well of the rear end portion of the chamber, so removing almost all the force applied to the needle by the main spring and hence almost all the pressure by the needle on the gristle or bone. As a result, the needle does not become embedded and blocked and liquid can continue to be ejected from the needle and a full dose, or substantially a full dose, administered.

This action of the deformable plunger will normally reduce either bone damage or the possibility of damage to the needle while in the body.

According to a preferred feature of the invention, the chamber is a sealed collapsible capsule having the noncollapsible rear end portion constructed on its rear end. The capsule may be fabricated of a deformable metal, plastics, or rubber material and preferably is cylindrical with a circumferentially ,corrugated side wall. The chamber may, however, be constituted by a tube having a sealed, puncturable forward end and a spring-loaded piston, the piston embodying the said non-collapsible rear end portion.

The storage life of this type of syringe is not as `dependably long, and is probably more susceptible to variation due to climatic changes than the capsule type syringe. Another advantage of the capsule type syringe is that the expandable capsule may be supplied from the fillers and loaded into the syringe where required, thus saving the expense of either an expandable syringe or the return of the syringe to the fillers.

The deformable plunger is conveniently shaped as a cup whose side wall has a plurality of projections or bulges which bear on to the entrance to the well, whereby when the plunger is subjected to a resistance f predetermined magnitude during forward travel of the needle the side wall and projections buckle inwards and the plunger passes in the well.

The interior of the chamber is filled with a liquid medicament. The rear end portion is not filled, and the small volume of air left in this facilitates the commencement of an injection operation, when the needle is piercing the forward end. The dosage of the chamber, less than its actual content will be about the same whether or not the plunger has been deformed.

The invention is effective in considerably reducing the number of casualties arising from the use of hypodermic syringes of this type and in providing syringes which can be relied on to give complete doses of medicament in a far higher proportion of injections than before. Still further improvement has been attained however by incorporating a secondary spring in the syringe to act against the forward end of the chamber and modify the action of the needle in such a manner that, although liquid is still discharged as the needle penetrates into the flesh, the hazard of needle blockage is substantially eliminated and the overall penetration of the needle is reduced. According to another feature of the invention, therefore, a hypodermic syringe comprises a casing, a main spring located in the casing behind the chamber and acting on a rearward end of the chamber, a release mechanism in the casing for retaining the main spring until it is released, a hypodermic needle through which liquid can pass and which prior-to-use is disposed through almost the full length of the interior of the chamber with its point directed to the forward end of the chamber, a secondary spring set between the casing and the forward end of the chamber so as to be able to urge the forward end of the chamber in a rearward direction, the main spring means having sufficient power and throw, when released, to drive the rearward end of the chamber forward against the reaction of the secondary spring and to contract the chamber and inject the needle and some liquid therethrough into the body of the user, and the secondary spring being sufficiently powerful thereupon to drive the forward end of the chamber rearward until the complete dose of liquid is injected and the secondary spring is in equilibrium with the main spring means.

It will be appreciated that the provision of a release mechanism which can release two detached springs acting on the far ends of a chamber or capsule would be a most undesirable complication in a compact instrument of this type and a further advantageous feature of a hypodermic syringe in accordance with the invention is that a release mechanism is not required to hold the secondary spring prior-to-use. The main spring means is arranged to have initially a greater loading than that of the secondary spring so that when released it can drive the chamber towards the skin of the user and commence the contraction of the chamber and penetration of the needle into the fiesh against the reaction of the opposing secondary spring. The rate and initial loading of the main spring must however be such that the loading of the main spring decreases to that of the opposing secondary spring before the chamber is fully contracted and the needle fully advanced into the flesh. Because of the inertia in the rapidly moving chamber and spring system the needle overshoots the position it would be in when there is static equilibrium between the two opposed springs. Consequently the complete construction of the chamber is effected by a simultaneous advance of both springs which involves a small reciprocation and hence slight withdrawal of the needle before the injection of liquid is completed, from its limit of penetration when the system overshoots the final equilibrium position.

If the hypodermic syringe incorporates both the deformable plunger and the secondary spring, the magnitude of the resistive force at which the member is arranged to deform may be higher than if the secondary spring is not incorporated. This is because the secondary spring will perform two functions. Firstly it will withdraw the needle a little. If and when the needle impinges on gristle facia during its throw it will be rapidly withdrawn sufficiently to relieve pressure on the facia and prevent this from blocking the needle. Secondly it limits the maximum penetration of the needle and thus decreases the likelihood of the needle contacting the bone. The injector is thus rendered even more effective and safer to use than its predecessors. By judicious choice of the throws and strengths of the main spring means and the secondary spring and of the prior-to-use position of the chamber in the casing either the maximum penetration of the needle can be considerably limited so that the injection may be simply hypodermic rather than intra muscular, or the amount of withdrawal of the needle from maximum penetration can be increased.

The forward end of the chamber may be held by the secondary spring in position to the rear of the forward end of the casing, and the main spring means may have also sutiicient loading, when released, to drive the whole chamber forward to contact the body of the user positioned at the forward end of the syringe, and thereby to increase the loading of the secondary spring. Then, in operation, the needle can acquire a considerable momentum before it strikes the skin, to facilitate the injection of the needle.

According to yet another feature of the invention, the said main spring means and the release mechanism comprise a compression spring, a main plunger having a sleeve part located within the casing and having a recess, a detent body integral with the casing and having a detent which can engage in the recess in the plunger, a member having a push button projecting from the rear end of the casing and a shaft within the casing for holding the detent in engagement with its recess in the plunger, the shaft having a recessed portion which can be aligned with the detent when the push button is pressed whereby the detent can move out of engagement with its recess and the plunger and main compression spring released.

The casing of a syringe in accordance with the invention can be advantageously made detachable into two parts, a rear part housing the main spring and the release mechanism and a forward part housing the chamber and the secondary spring, so that after use of the syringe the casing may be so detached and the main spring and the chamber reloaded.

Three different types of hypodermic syringes in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE l is a sectional elevation in a prior-to-use position of one type of syringe having a secondary spring and a liquid-containing capsule;

FIGURE 2 is a sectional elevation of this syringe partway through an injection operation;

FIGURE 3 is an outline and part-sectional elevation of the syringe after an injection;

FIGURE 4 is a sectional elevation of the liquid-containing capsule;

FIGURE 5 is an end view of the deformable plunger in the liquid-containing capsule;

FIGURE 6 is a sectional View of a second type of syringe without a secondary spring and with a liquid-containing capsule when in a prior-to-use position, while FIGURE 7 is a sectional view of a third type of syringe without a secondary spring and with a liquid-containing chamber when in a prior-to-use position.

The syringe as shown in FIGURE l has a casing which is detachable into two parts, a forward housing 1 and rear housing 2, having bores 3 and 4 in each respectively. The bore 3 has opposing steps S and 6 located respectively further from and nearer to the join in the housings 1 and 2, and the bore 4 has a step 7 at its forward end.

A tubular capsule carriage 8 has an external flange 9 on one end and an internal flange at the other, and is arranged within the forward housing 1 with the flange 9 resting on the step 6 so that the remainder of the carriage 8 is forward of the flange 9. A secondary spring 11 is housed in an annular space between the capsule carriage 8 and the bore 3 between the step 5 and the flange 9. The length of the carriage 8 is such that the free end of the forward housing 1 extends beyond the flange 10 in the position described. The capsule carriage 8 is thus movable away from the step 6 and against the spring 11. A capsule 12, with a pot 13 sealed onto one end to form a noncollapsible rear end portion of the capsule, is located within the capsule carriage 8 with its forward end resting on the flange 10.

A tubular main carriage 14 has an internal flange 15 at its forward end and an external flange 16 having detent holes 17 at the other. The external diameter of its body is such that it will travel within the capsule carriage 8 while its flange 16 is arranged to travel within the bore 4 of the rear housing 2 and the flange 15 passes over the pot 13 and bears on to the end of the capsule 12. A tubular top hat-shaped plunger 18 inside the main carriage 14 also fits over the pot 13 with its external flange resting on the internal face of the flange 15. A main spring 19 is located within the carriage 14 and has one end bearing on the external flange of the plunger 18 and the other on the face of a detent body 20 fixed at the rear end of the rear housing 2. The initial loadings and the rates of the two springs 11 and 19 are such that the loading of the main spring 19 will decrease during use to equal the consequential loading of the secondary spring 11 before the capsule 12 is fully collapsed. The initial loading of the main spring 11 must be sufllcient to rapidly move the capsule 12 forward to the skin, increasing the loading of the secondary spring 11 at the same time, and partially collapse the capsule. The final equilibrium position of the two springs is that shown in FIGURE 3.

The detent body 20 has an axial bore 21 and its external shape also forms an annular space, within the rear housing 2, in which may travel the external flange 16 of the main carriage 14, and which is connected to the bore 21 by detent holes 22 corresponding to the holes 17 in the flange 16 so that the added length of a hole 17 and 22 is less than or equal to their diameter. A push button 23 extending into the detent body 20 has a spindle 24 with an annular recess 25 whose depth is equal to or greater than the thickness of the flange 16 of the main carriage 14. A seating 26 is attached to the spindle 24 where it protrudes through the detent body 20 into the rear housing 2. A release spring 27 is provided, housed within the main spring 19, and having its ends bearing on the seating 26 and the end of the plunger 18.

The spindle 24 slides within the bore 21 of the detent body 20, and the function of the release spring 27 is to retain the push button 23 is a loaded position prior-to-use with the button protruding rearwards from the detent body 20 and the rear housing 2, and with the spindle 24 opposite and covering the detent holes 22. The recess 25, being between the spindle 24 and the button 23, also protrudes from the end of the detent body 20. Balls 28 of diameter just less than or equal to the added length of the holes 17 and 22 are held in the added holes 17 and 22 by the bore 4 and the spindle 24. Thus the balls 28, backed by the spindle 24, form a detent to hold the main carriage 14 and hence the main spring 19 in the compressed position. A protective cap 29, retained by a recess between the detent body 20 and the rear housing 2, serves to prevent accidental firing of the syringe as a result of knocks etc.

FIGURES 4 and 5 clearly show the collapsible construction of the capsule 12 and the manner in which the pot 13 is sealed on to the rear end of the capsule. The

interior of the pot 13 is a well 13a. A cup-shaped plunger 30 is lodged in the mouth of the well 13a and has longitudinal projections or bulges 31, the maximum outside diameter of which is just greater than the bore of the well 13, whereas the diameter of the plunger between the bulges is a little less than the bore of the well 13. The plunger is so shaped and constructed that on application of a given force to the member 30 by the needle, projections 31 buckle inwards to completely clear the bore of the well 13a and the member is driven into the well 13a. The hollow interior of the member 30 communicates with the well 13a by a hole 32. The construction of the plunger 30 is more clearly shown in FIGURE 5 which is -a view looking rearward on the member alone. The shape of the projections 31 can be clearly seen. The interior of the plunger 30 is square-shaped just forward of the hole 32. The head of a hollow needle 33 rests on the sides of the square in the well in the member 30 and is retained in a position along the axis of the capsule 12 with its point resting against the forward face of the capsule by a retaining ring 34. The cylindrically corrugated wall of the capsule 12 is made of tin. A rubber pad 35 fits onto the forward end of the capsule.

The capsule is almost filled with a liquid medicament leaving only the well of the plunger 30 around the head of the needle 33 and the well 13a containing air. Liquid being incompressible, the presence of a little air allows the commencement of capsule collapse, and the penetration of the needle 33 into the skin before ejection of the solution and the continuation of solution ejection after the capsule 12 has been fully collapsed. The capsule unit is thus self-contained and it can be supplied as a refill to the syringe, with its contents sterilised. The capsule fits into the syringe in the position shown in FIGURE l with the rubber pad 35 acting as a locating cushion between the forward end of the capsule and the internal surface of the flange 10 of the capsule carriage 8. The pad 35 also protrudes through the flange 10 to rest on the skin during firing.

When the syrin-ge is required for use the protective cap 29 is removed and the syringe is held, thumb over the button 23 with the forward end against a fleshy part of the body. The button is pressed so as to bring the recess 2S opposite the detent holes 22 in the detent body 20. The balls 28 are impelled to the recess 25 and the main carriage 14 moves rapidly forward by the expansion of the main spring 19 acting on the external flange of the plunger 18. The capsule 12 together with its liquid contents is arranged in its initial state -to be stiffer than the comparatively unloaded secondary spring 11, and because of this, the inertia of the system, and the pressure inside the sealed capsule the expansion of the main spring 19 moves the capsule 12 and the capsule carriage 8 with the main carriage 14, compressing the spring 11, until the pad 35 contacts the skin. Normally, by this time capsule 12 has started to collapse and the needle 33 has pierced the end wall, because of relative inertia and the loading of the secondary spring 11, further movement of the forward end of the capsule 12 is then prevented, and the capsule 12 continues to collapse under the force of the main spring 19 and the point of the needle 33 pierces the rubber pad 35 and enters the skin. The disposition 0f the injector parts is now as shown in FIGURE 2. The injection of solution commences and continues as the main spring 19 continues to expand and the capsule 12 is further collapsed and the needle 33 driven deeper into the flesh. The passage of the medicament is facilitated by the provision of the square portion of the well in the member 30. The liquid passes between the corners of the square and the head end of the needle 33. The main spring 19 overshoots the equilibrium position of the two opposing springs 11 and 19 and through the reaction of the secondary spring 11, acting through the carriage 8, the spring-capsule system reciprocates rapidly causing slight withdrawls of the needle as the two opposing springs act in consort to complete the collapse of the capsule. The rearward movement of the forward end of the capsule caused by the secondary spring limits the maximum penetration of the needle. The nal disposition of the injector parts is then as shown in FIGURE 3. The final discharge of liquid is aided by expansion of the small volume of air in the capsule initially compressed by the commencement of `the capsules collapse, and the withdrawal of the needle prevents the needle from being blocked by gristle facia.

If the syringe is inadvertently used at a part of the body where the penetrating depth of the needle is greater than the depth of the flesh, and the needle is caused to strike a bone, the sudden loading on the needle is transmitted to the cup-shaped plunger 30, whose projections 31 then buckle inwards and allow the pot 13, driven by the main spring 19, to ride over the member without causing any further force to be applied to the needle. The injection of solution will, however, continue.

The syringe may be reloaded with a fresh capsule after use by detaching the forward housing 1 from the rear housing 2 and pushing the collapsed capsule 12 rearwards from its carriage 8. The rnain carriage 14 is pushed into the rear housing 2 to compress the springs 19 and 27 so that when detent holes 17 and 22 are again opposite each other as in FIGURE 1 the release spring 27 will force the button 23 outwards. This causes the balls 28 to leave the recess 25 and move into the combined holes 17 and 22 and grip the main carriage 14 in the prior-to-use position by means of the spindle 24. The cap 29 is then replaced over the button 23. A new capsule 12 with pad 35 tted is dropped into the carriage S of the housing 1 and the two housings 1 and 2 are again joined. The syringe is then loaded, ready for use, as shown in FIGURE 1.

The particular syringe illustrated in the FIGURES 1 to 4 and described above has the following specification. It is 4.72 long, and uses a tin-walled capsule 1.897" long. The capsule has a non-collapsible pot about 1/2 in length and its collapsible portion collapses to just under 1/2 in length. Its main spring 19 is 3.94 in free length, has an initial loading of 18.7 lbs. and a rate of 9 l=b./in., while the secondary spring 11 is 1.95 in free length, has an initial loading of 8.55 lbs. and a rate of 14% lb./in. The resulting maximum penetration of the needle is limited to approximately 3A". The plunger 30 is made of tin and constructed to deform when it sustains through the needle 33 an applied force of between 6 and 8 lbs. The well 13 as shown in the FIGURE 5 has a diameter of 0.165 in. at its entrance tapering slightly to 0.163 in. at its rear end. The plunger 30 has an external diameter of 0.156 in. at its rear end, `and the dimension across diametrically opposite projections 31 is 0.177 in. The bore of the plunger 30 is 0.136 in., and the basic external diameter of the wall without the projection 31 is 0.156 in.

The syringe shown in FIGURE 6 uses a sealed collapsible capsule but does not have a secondary spring. The construction and contents of the rear casing 2 are similar to those of the syringe described above. The casing 1 has, however, a constant bore 40 in which the carriage 14 is a slide iit. The casing has an annular internal flange 41 at its forward end against which abuts the pad 35 and hence the forward end of the capsule 12. The release mechanism of this syringe operation in a manner similar to that of the syringe described with reference to FIGURES 1 to 4 but in this case capsule 12 is simply collapsed against the flange 41 by the main spring 19. The needle is similarly injected forwards until it encounters a resistance sufficient to deform the plunger.

The syringe shown in FIGURE 7 does not use a collapsible capsule or a secondary spring. In this syringe the casing 1 is lined with a stainless steel, or inert plastics material, tubular sleeve in which a plunger assembly 51 is adapted to slide as a tight slide fit. The plunger assembly 51 comprises the non-collapsible rear end pot 13 and the member 30 supporting the needle 33 as described earlier. The pot 13 is surrounded by a rubber piston 52 bearing against the inside of the sleeve 50. The casing 1 has an internal flange 41 similar to that shown in FIGURE 6 at its forward end and is seated by a bung 53 which has a guide channel for the needle 33. The construction and contents of the casing 2 are similar to those described with reference to FIGURES 1 to 4 and 6, but the carriage 19 is modified to bear on the rear end of yboth the piston 52 and the pot 13 and to seat both the springs 19 and 27. The chamber formed by the sleeve 50, the plunger assembly 51 and the bung 53 contains the liquid medicament.

This syringe is operated in a manner similar to the two other types described above. When released, the carriage 19 urges the plunger assembly 51 forwards so that the needle pierces the bung 53 and injects medicament as before.

The syringe described with reference to FIGURE 7 could of course be constructed with a secondary spring is desired.

We claim:

1. A hypodermic syringe comprising a casing, a liquidcontaining chamber within the casing and having a puncturable forward end and a non-collapsible rear end portion, main spring means within the casing which can drive the said rear end portion of the chamber forward when released, means for holding said main spring in a compressed condition, and main spring release means, the said rear end portion having a tubular well which opens into the chamber, a deformable plunger located in the entrance to the well, and a hypodermic needle which prior-to-use is disposed through almost the full length of the interior of the chamber with its point directed to the puncturable forward end and its head accommodated in the deformable plunger whereby it can be driven forward when the main spring is released, the plunger being deformed and displaceable into the tubular well when the needle is subjected to a given resistance to its forward travel.

2. A hypodermic syringe according to claim 1 wherein the deformable plunger is shaped as a cup whose side wall has a plurality of projections which bear onto the entrance to the well, whereby when the plunger is subjected to the given resistance the lside wall and projections buckle inwards and the plunger may pass into the well.

3. A hypodermic syringe comprising a casing, a liquidcontaining sealed collapsible capsule within the casing with a puncturable forward end and a non-collapsible rear end portion, releasable main spring means within the casing which can drive said rear end portion forward when released, means for holding said main spring in a compressed condition, and main spring release means, said rear end portion having a tubular well which opens into the capsule, a deformable plunger located in the entrance to the well, and a hypodermic needle which prior-to-use is disposed through almost the full length of the interior of the capsule with its point directed to the puncturable forward end and its head accommodated in the deformable plunger whereby it can be driven forward when the main spring is released, the plunger being deformed and displaceable into the tubular well when the needle is subjected to a given resistance to its forward travel.

4. A hypodermic syringe according to claim 3 wherein the capsule is cylindrical and the collapsible portion has a circumferentially corrugated side wall.

5. A hypodermic syringe according to claim 1 wherein the said main spring means is a compression spring, and said holding means and said release means comprising a main plunger having a sleeve part located within the casing and having a recess, a detent body integral with the casing and having a detent which can engage in the recess in the plunger, a member having a push button projecting from the rear end of the casing and a shaft within the casing for holding the detent in engagement with its recess in the plunger, the shaft having a recessed portion which can be aligned With the detent when the push button is pressed whereby the detent can move out of engagement with its recess and the plunger and main compression spring released.

6. A hypodermic syringe according to claim 3 and wherein the casing is detachable into two parts, a rear part housing the main spring and a forward part housing the capsule so that after use of the syringe the casing may be so detached and the main spring reloaded and the spent capsule replaced with a new one.

'7. A hypodermic injector according to claim 3 having a secondary spring set 'be-tween the casing and the forward end of the capsule so as to be able to urge the forward end of the capsule in a rearward direction, the main spring means having sufficient power and throw, when released, to drive the rearward end of the capsule forward against the reaction of the secondary spring and to compress and partially collapse the capsuleand inject the needle and some liquid therethrough into the body of the user, and the secondary spring being sufficiently powerful to thereupon drive the forward end of the capsule rearward until the collapse of the capsule is completed and the secondary spring is in equilibrium with the main spring means.

8. A hypodermic syringe according to claim 7 and wherein the said collapsible capsule is housed in the forward end of the casing with its forward end behind the forward end of the casing, the said main spring means having suicient power and throw, when released, to commence its driving action by driving the whole capsule forward to contact the 'body of the user when positioned at the forward end of the syringe whilst increasing the loading of the secondary spring.

9. A hypodermic syringe according to claim 7 wherein the said main spring means is a compression spring, and said holding means and said release means comprising a main plunger having a sleeve part located within the casing and having a recess, a detent body integral with the casing and having a detent which can engage in a recess in the plunger, a member having a push button projecting from the rear end of the casing and a shaft within the casing for holding the detent in engagement with its recess in the plunger, the shaft having a recessed portion which can be aligned with the detent when the push button is pressed whereby the detent can move out of engagement with its recess and the plunger and main compression spring released.

10. A hypodermic syringe according to claim 7 wherein the casing is detachable into two parts, or rear part housing the main spring and a forward part housing the capsule and the secondary spring, so that after use the casing may be so detached and the main spring reloaded and the spent capsule replaced with a new one.

References Cited UNITED STATES PATENTS 2,752,918 7 195 6 Uytenbogaart.

, FOREIGN PATENTS 915,262 1/1963 Great Britain. 964,585 7/1964 Great Britain.

RICHARD A. GAUDET, Primary Examiner.

W. E. KAMM, Assistant Examiner.

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