1,149,042. Hypodermic injection apparatus. DEFENCE SECRETARY OF. 8 March, 1966 [11 Dec., 1964], No. 56018/68. Divided out of 1149041. Heading A5R. A hypodermic syringe comprises a syringe casing having a forward end for contacting a patient, a liquid-containing sealed collapsible capsule which has a puncturable forward end and which is housed in a forward end portion of the casing, a hypodermic needle through Which liquid can pass and which prior to use of the syringe is disposed through almost the full length of the interior of the capsule with its pointed end directed to the forward end of the capsule, main spring means located in the casing behind the capsule to act on the rear end of the capsule, a release mechanism located in the casing to retain the main spring means until it is released, and a secondary spring positioned between the casing and the capsule in a manner such that it is capable of urging the forward end of the capsule in a rearward direction; the main spring means has sufficient power and throw, when released, to drive the rear end of the capsule forward against the reaction of the secondary spring and to compress and partially collapse the capsule thereby to inject the needle and some of the liquid in the capsule into the body of the patient, the secondary spring being sufficiently powerful thereupon to drive the forward end of the capsule rearwards until the collapse of the capsule is completed. The forward end of the capsule preferably is held by the secondary spring in a position to the rear of the forward end of 'the casing, the main spring means having sufficient power and throw, when released, initially to drives the whole capsule forward to contact the body of a patient positioned at the forward end. of the casing of the syringe whilst simultaneously increasing the loading of the secondary spring. The casing preferably is detachable into two parts, a rear part housing the main spring means and the release mechanism and a forward part housing the capsule and the secondary spring, whereby, after use of the syringe, the two parts of the casing may be separated, the main spring means reloaded, and the spent capsule replaced with a new capsule. As illustrated in Figure 1, the syringe comprises a casing which consists of a forward housing 1 and a rear housing 2. Situated in the bore 3 of the forward housing is a tubular capsule carriage 8 provided with an external flange 9, which rests against a step 6 provided at the rear end portion of the forward housing, and with an internal flange 10. Situated in the annular space between the capsule carriage and the forward housing is a secondary spring 11 one end of which rests against the external flange of the capsule carriage and the other end of which rests against a step 5 provided at the forward end portion of the forward housing. Situated within the capsule carriage is a liquid-containing sealed collapsible capsule having a circumferentially corrugated side wall 12 made for example of tin. Sealed to the rear end of the capsule is a non-collapsible portion 13; extending about the puncturable forward end of the capsule is a rubber pad 35 which rests against the internal flange of the capsule carriage. Situated in the bore 4 of the rear housing is a tubular sleeve or main carriage 14 provided with an external flange 16, which cooperates with a step 7 provided at the forward end portion of the rear housing to limit the axial movement of the main carriage, and with an internal flange 15 which bears on the rear end of the capsule. Situated within the main carriage to extend about the non-collapsible portion of the capsule is a tubular plunger 18 having an external flange which rests against the internal flange of the main carriage. Fixed to the rear housing at the rear end thereof is a detent body 20 having an axial bore 21 in which is located a shaft comprising a front end portion which provides a seating 26, a spindle portion 24, a recessed portion 25 and a rear end portion which provides a push button 23. Situated within the main carriage to extend about the plunger is the main spring means in the form of a compression spring 19 one end of which rests against the detent body and the other end of which rests against the external flange of the plunger. Situated within the compression spring is a release spring 27 one end of which rests against the seating provided on the shaft and the other end of which rests against the rear end of the plunger. The external flange of the main carriage is provided with detent holes 17 and the detent body is provided with detent holes 22; situated in the detent holes are balls 28 which are retained in position prior to operation of the syringe by the spindle portion of the shaft thereby to prevent axial movement of the main carriage under the influence of the main compression spring. Depression of the push button against the action of the release spring brings the recessed portion of the shaft into alignment with the aligned detent holes thereby to allow the balls to move radially out of the detent holes provided in the external flange of the main carriage and into the recessed portion of the shaft whence the main carriage may move axially under the influence of the main compression spring to initiate collapse of the capsule. Prior to operation of the syringe, a protective cap 29 is located about the push button to prevent accidental operation of the syringe. As described and illustrated, the capsule used in the syringe is the liquid-containing sealed collapsible capsule which is disclosed and claimed in Specification 1149041. Such capsule, which includes a hypodermic needle adapted for passage of liquid therethrough and disposed, prior to discharge of the capsule, through almost the full length of the interior of the capsule, has a puncturable forward end to which a pointed forward end of the needle is directed and a rear end which has a non- collapsible portion defining a tubular well opening into the capsule; positioned in the entrance to the well to bear on the rear end of the needle to hold the needle away from the rear end of the capsule is a deformable plunger which is displaceable into the well by the rear end of the needle if the needle is subjected to a predetermined axial force, for example as a result of contacting gristle or bone during an injection operation. The plunger may be cup-shaped and have a side wall provided with a plurality of projections or bulges such that the maximum outside diameter of the plunger is just greater than the bore of the well in the non-collapsible portion of the capsule; the side wall is capable of buckling to allow the plunger to be displaced into the well.