A hypodermic syringe comprising a housing having a needle chamber and a sealed receiving chamber containing an injection liquid. A hollow needle is mounted for slidable displacement in the needle chamber in a retracted position. A first piston acts on the hollow needle for displacing it to an extended position in which the needle projects from the housing for piercing the skin. A second piston in the receiving chamber acts on the injection liquid to pressurize the same. An apparatus holds the first and second pistons in respective retracted position with a passage connecting the first and second chambers and also being provided with a closure normally closing the passage. An actuator releases the holding apparatus to permit the first and second pistons to move to respective extended positions in which the hollow needle is displaced to its extended position and the injection liquid is pressurized whereby the closure is positioned in the path of travel of the hollow needle for being rendered inoperative thereby in its travel to the extended position whereupon the passage establishes communication between the receiving chamber and the hollow needle whereby injection liquid flows from the receiving chamber to the hollow needle under the pressure applied to the injection liquid by the second piston.

BACKGROUND OF THE INVENTION 
The present invention relates to a hypodermic syringe having within its 
housing a receiving chamber for an injection liquid which can be placed 
under pressure by a piston or the like and having a hypodermic needle. 
Disposable syringes of this type are known in which the needle must be 
screwed onto the syringe in order to make it operable. The injection 
liquid is taken from ampules and aspirated into the syringe. The handling 
of such syringes is hygienically unobjectionable and furthermore it is 
time-consuming. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a hypodermic syringe of the 
aforementioned type which can be used immediately and satisfies all 
hygienic requirements. It is another object that the hypodermic syringe be 
simple to manufacture and so inexpensive that it can be used as a 
disposable syringe. 
In order to achieve this purpose, the hypodermic needle is arranged in a 
needle chamber which is associated with the reception chamber for the 
injection liquid and the needle can be displaced by a piston or the like 
from the needle chamber and can be connected with the receiving chamber in 
an operating position. 
It also resides within the scope of the invention to provide the injection 
needle with an inner space which widens out conically in the direction 
opposite the direction of the thrust of the piston and to arrange the 
needle within the injection liquid; furthermore, the needle is to be 
developed in such a manner that it can be transferred by the piston from 
the receiving chamber into an operating position. In this case the needle 
of the hypodermic syringe of the invention preferably lies within a 
cylindrical space in which the needle attached to the piston can be 
displaced by the force of a force accumulator and thereby emerges from the 
cylinder so as to assume the so-called operating position. The needle 
therefore comes out of its covering only when it is to be used and cannot 
be contaminated previously. This is true also in the case of the 
hypodermic needle which was first mentioned, in which the needle itself is 
arranged in a space separate from the liquid but completely covered and is 
filled with liquid only in the operating position. 
It has proven particularly favorable to arrange the injection needle in a 
bag which preferably contains the injection liquid. The tip of the needle 
perforates this bag when the needle is brought into the operating position 
and therefore when pressure is exerted on the piston. 
The piston which, in accordance with the invention, bears the needle and 
closes off the top of the liquid chamber is also under the pressure of a 
force accumulator in the same way as the other piston which is provided 
merely for the guidance of the needle and adjoining which, in accordance 
with another feature of the invention, a further piston for the ejection 
of the liquid is present in a neighboring space. The force accumulators 
are under tension in the position of rest of the syringe of the invention 
and are held by locking or closure elements which must be capable of 
operation in simple manner. For this there has proven to be particularly 
favorable a locking plate having a keyhole-like cutout which holds a head 
of a separate push piston. This push piston holds the force accumulator, 
developed as a coil spring, fast in its force-accumulation position so 
that this part of the syringe can be removed from the rest of the syringe 
without the danger of relaxation of the spring. It is also possible to 
make separate use again of this part of the syringe, which in accordance 
with the invention is arranged in a protective cap. 
In the case of the hypodermic syringe with separate needle and liquid 
chambers there may also be used, in accordance with the invention, a lever 
system which on the one hand holds a detent member of the needle piston or 
the push bolt and on the other hand the piston for the liquid fast, in 
which case--in accordance with another feature of the invention--the 
liquid piston is developed so that it can be released from the lever 
system with time delay for the liberation of the needle piston. As a 
result of this measure, the hypodermic needle is first engaged in its 
so-called operating position before it is acted on by liquid, which 
considerably broadens the field of use of the hypodermic needle of the 
invention and in particular prevents any problems with the so-called 
aspiration. 
Furthermore, it has proven favorable to develop the cylinder bottom of the 
reception chamber for the hypodermic needle of a material which can be 
perforated by the tip of the needle and which preferably also surrounds 
the needle in the form of a sleeve after the perforation, for instance in 
the manner of a rubber which lies against the needle. 
When the hypodermic syringe is provided with a liquid bag it is sufficient 
to provide an opening in the bottom of the cylinder, the edges of this 
opening serving as abutment for the bag upon piercing of the bag by the 
needle. 
If the syringe of the invention has two adjacent receiving chambers for 
needle and liquid then in accordance with the invention they are connected 
by an opening in the region of the cylinder bottoms and in the position of 
rest of the hypodermic syringe are temporarily separated from each other 
by a closure element, for instance a small sealing plate. The sealing 
plate is so developed that it is removed or crushed upon the impingement 
of the needle piston and thus provides a passage for the liquid which can 
then penetrate into the inside of the needle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A hypodermic syringe S for liquid medicaments or injection liquids F has, 
as shown in FIG. 1, a piston 2 within a cylinder 1, a hollow needle 
3--shown in exaggerated cross section in the drawing--extending from the 
piston into the cylinder chamber 4 which receives said injection liquid F. 
The inside 5 of the needle communicates with the cylinder chamber 4 by 
perforations 6. 
In the longitudinal axis A of the syringe, the head 9 of a slide bolt 11 
(FIG. 2) acted on by a spring 1 presses against the surface 8 of the 
piston remote from the needle. This coil spring 10 rests at the one end 
against the head 9 and at the other end against the inside of an abutment 
plate 12 which is part of a cap-like top 13 with cap chamber 14. 
Towards the top the push bolt 11 terminates in a bolt head 15 which, in the 
tensioned position of the coil spring 10 shown--and therefore in the 
position of rest of the hypodermic syringe S--is seated over a locking 
plate 16, namely over a slot 18 which is traversed by the shaft 17 of the 
push bolt (FIG. 4). Adjoining this slot is a cutout 19 which is larger 
than the cross section of the bolt head 15. The cutout 19 and the slot 18 
together form an opening of keyhole shape. 
If the locking plate 16 is moved in the direction of the arrow z from its 
locking position shown in FIG. 3, the coil spring 10 pulls the push bolt 
11 in the direction y of extension through the cutout 19 in the locking 
plate 16 and the tip 20 of the hollow needle 3 penetrates the cylinder 
bottom 21, the remainder of which rest snugly laterally as sleeves 22 
against the hollow needle 3. 
The liquid F which fills the cylinder space 4 when the hollow needle 3 is 
in the position of rest shown in FIG. 1 is pressed by the travel of the 
piston 2 through the hollow needle 3 until the piston 2 rests against a 
lower annular shoulder 23; the inside 5 of the needle is then completely 
closed off. 
In the embodiment shown in FIG. 5, the liquid F is arranged in a sack 30 
which is fixed partially to the wall 1 of the cylinder or--not shown in 
the drawing--can be closed via the piston 2. Upon the unlocking of this 
syringe S.sub.1, the tip 20 perforates the bag 30 in the region of a lower 
opening 31 in the bottom of the cylinder; the bag 30 is held in the 
cyinder 1 by the cylinder bottom 21 which in this case is of ring shape. 
The hypodermic syringe S.sub.2 of FIG. 6 consists of two receiving chambers 
4,40 with parallel longitudinal axes A, B. The one receiving chamber 4 
contains the hollow needle 3, in this case without the injection liquid F, 
which is arranged in the parallel reception chamber 40. 
After the removal of a protective cap 39, the bolt head 15 is released by 
pressure (arrow x) (FIG. 7) on a lever lock 38 and the piston 2.sub.h --in 
this case hollow--is guided by the spring 10 down to the bottom 21 of the 
cylinder, a lateral seal 41 being thereby destroyed; this seal closes a 
passage 42 to the adjacent receiving chamber 40 which is connected with 
the inside 5 of the needle by perforations 43 in the hollow piston 
2.sub.h. The liquid F immediately flows into the inside 5 of the needle 
under the pressure of a piston 44 which is acted on by a spring 48. 
In the position of rest shown in FIG. 6 an axial guide bar 45 of the liquid 
piston 44 holds a hook 36 by the pressure of a driver 46 against a tilt 
lever 35 under the bolthead 15--and thus holds the latter in locking or 
closed position. With a time delay as compared with the lowering of the 
push bolt 11 the tilt lever 35 detaches itself from the guide rod 45 so 
that the latter releases the liquid piston 44. The time delay can be 
produced, for instance, by slotted-link elements, not shown. 
The hypodermic syringe S or S.sub.1 consists essentially of two parts which 
can easily be separated from each other, namely the lower syringe part 1 
with needle 3 and liquid F and the upper push part with the spring 10 
tensioned on the push bolt 11 and the locking device 16. The two parts can 
be connected with each other in the region 25 by a screw thread and thus 
be detached from each other. 
The hypodermic syringe S.sub.2 is of a correspondingly simple construction. 
In order to permit a slow displacement of the liquid piston 44, the shaft 
45 thereof can furthermore be provided with a hand grip 50 which in its 
turn has a shaft 49.