US 3797487 A
A hypodermic syringe by which aspiration as well as injection can be effected, for example for the purpose of testing to see if the cannula has been inserted into a correct tissue of the patient. The syringe includes an operating lever for engaging a clutch acting between the piston rod or plunger of the syringe and a slide mounted co-axially on the piston rod and slidable thereon in a housing formed by part of the body of the syringe. The clutch can be released or engaged by the user while he is gripping the piston rod with the same hand, and thereby he can readily control the aspiration volume.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Schmidt HYPODERMIC SYRINGE WITH CLUTCH FOR ASPIRATION  Inventor: Gunther Schmidt, Eschwege,
Germany  Assignee: M. Woelm, Eschwege, Germany  Filed: Oct. 27, 1971  Appl. No.: 192,990
 Foreign Application Priority Data Oct. 29, 1970 Germany ..l 2053096 Apr. 22, 1971 Germany 2119508  US. Cl. 128/218 R, 128/218 PA  Int. Cl A6ln 5/22  Field of Search 128/215,218 R,218 P, 128/218 PA, 218 D, 218 F, 2 F, DIG. 5, 276,
 References Cited UNITED STATES PATENTS 2.585815 2/1952 McLintock 128/218 C 1.718.596 6/1929 Smith 128/218 D 3.583.399 6/1971 Ritsky... 128/218 D 3224.445 12/1965 Melott 128/218 D [4 1 Mar. 19, 1974 2,892,457 6/1959 Sturtz 128/218 R 3.340.872 9/1967 Cox 128/218 D 3.528,404 9/1970 Chan 128/276 X 3,035,605 5/1962 Ninnelt 222/153 X FOREIGN PATENTS OR APPLICATIONS 1,278,702 9/1968 Germany 128/218 R 31,681 12/1926 France 128/218 D Primary ExaminerRichard A. Gaudet Assistant Examiner--J. C. McGowan Attorney, Agent, or F irm-Salter & Michaelson 5 7 ABSTRACT A hypodermic syringe by which aspiration as well as injection can be effected, for example for the purpose of testing to see if the cannula has been inserted into a correct tissue of the patient. The syringe includes an operating lever for engaging a clutch acting between the piston rod or plunger of the syringe and a slide mounted co-axially on the piston rod and slidable thereon in a housing formed by part of the body of the syringe. The clutch can be released or engaged by the user while he is gripping the piston rod with the same hand, and thereby he can readily control the aspiration volume.
16 Claims, 12 Drawing Figures PAIENIEBMAR 19 1974 SkiEH 2 BF 4 Pmmwm 1 9 mm shame? SHEEI M 0? 4 HYPODERMIC SYRINGE WITH CLUTCH FOR ASPIRATIQN The invention concerns a hypodermic needle of the kind having means for aspiration, provided with a swivelling operating lever at the handle end of the syringe housing, the operating lever being movable into engagement with the piston rod for aspiration against the force of a return spring.
In the case of repeated injections it is necessary for medical reasons for the person giving the injections to make sure, after penetrating with the injection cannula that the correct tissue was entered. This is done by aspiration immediately after puncturing. For this purpose, the piston of the syringe is pulled back slightly thus drawing blood from the body to obtain an idea, by observing the type and quantity of blood, in which tissue the point of the cannula is located. Injection can only be made after a blood check by aspiration.
Aspiration with commercial-type hypodermic syringes presents difficulties particularly in cases where specially sensitive tissues must be punctured and also when relatively restricted space is available for handling the syringe. This is a regular experience in medicine.
In a hypodermic syringe of a known type, a doublelever is arranged on a swivel pin located in a slot on the finger grip piece of the syringe housing, extending at an acute angle to the piston rod axis of the syringe in such a way that the swivel bearing is moving in the slot towards the piston rod. The piston rod is also provided with teeth over which one end of the double-ended lever can be engaged against the force of a spring, by pressing on the other arm of the double-ended lever. In a known design, a danger exists of the aspiration lever jamming against the piston rod of the syringe during operation.
It is also known to provide a spring on the piston rod of a syringe, the spring acting together with an opposing bearing which is connected with the piston rod over a friction connection. In this case, the spring is preloaded when the piston rod is pushed forward, the preloading force corresponding to the friction force of the connection with the piston rod. If the grip is released on the piston rod of such a syringe, the piston of the cylindrical ampoule is pulled back under spring pressure and aspiration thus takes place. The disadvantage of this syringe lies in the fact that friction is acting against the movement of the piston rod during the whole injection process and also in that pre-tensioning of the spring is a necessary condition for the aspiration movement, pre-tensioning only being capable of being performed by shifting the piston rod in the direction of the injection movement.
Furthermore, a syringe with an aspiration device is known in which a further axially movable rod is arranged parallel to the piston rod, at the syringe housing. The piston rod and the rod arranged parallel to it are both provided with teeth and are coupled by a reversing gear. By pressing on the parallel rod, the piston rod can be pulled back thus producing aspiration. Such an arrangement requires a great deal of space and a further disadvantage is presentedby the fact that the rod extending parallelto the piston rod is moving to the outside at the same speed as the piston moves inwards during injecting.
The purpose of the invention is to create a hypodermic syringe of the aforesaid kind which would allow aspiration with the piston rod in any position without the danger of jamming or blocking and ensure afree movement for the piston rod during injection.
According to the invention, a hypodermic syringe having means for aspiration and including a piston rod, a return spring therefor and an operating lever engageable in the piston rod to move the piston rod against the force of the return spring for the purpose of aspiration also includes a slide slidable on the piston rod on movement of the operating lever and clutch means provided between the slide and the piston rod.
Conveniently the slide is a frusto-conical bore widening towards the end of the piston rod to be gripped by the user and the syringe also includes a plurality of balls acting as clutch elements and positioned in the annular space between the frusto-conical bore of the slide and the piston rod, said balls being urged to grip the piston rod by wedging action of the frusto-conical bore on axially moving the slide in the direction to reduce the radial clearance between the bore and the piston rod, and a stop member which extends into the conical bore when the slide has been moved to the position in which the balls are freed from engagement between the piston rod and the frusto-conical bore and resilient means for urging the balls into engagement with the stop member, which thereby forms a support for the balls when-the clutch means has been released.
The syringe may include a housing into which the slide is movable, said housing provided with diametrically-opposite slots extending axially of the housing and each receiving stub shafts pointing in opposite directions to each other on the operating lever, said stub shafts extending through the slots in the housing into blind holes in said slide.
The fulcrum of the operating lever may be provided by a fixed abutment against which the lever swivels and spaced from the axis of said stub shafts. The fixed abutment may be positioned between the stub shafts and the end of the lever to be engaged by the user. The operating lever may alterantively be a double-arm lever and said fixed abutment may be engaged by the end of the operating lever remote from that end which is to be gripped by the user. Conveniently the operating lever may include a frame part of substantially rectangular shape surrounding the slide housing. The operating lever may be pivotally mounted on the slide housing at the end of the lever remote from the end thereof which is to .be gripped by the user and said slide may include tenons engaging the lever in such a way that the clutch is engaged when the lever is pulled towards the end of the piston rod that is gripped by the user.
The syringe may include spring means acting to urge the slide in the direction in which said clutch means is released.
The syringe may include a pair of fixed stops between which the slide is movable.
Several versions of hypodermic syringe of the aforesaid kind in accordance with the invention, are illustrated in the accompanying drawings and are described in detail with reference thereto. In the drawings:
FIG. 1 shows a side view of a hypodermic syringe with an aspiration device having a cylindrical ampoule;
FIG. 2 shows the same view as in FIG. 1 except that part of it is shown in section;
FIG. 3 shows the head of the syringe shown in FIGS. 1 and 2 in the normal working position from which aspiration can be effected with the piston rod in any position;
FIG. 4 shows the same view as FIG. 3 but with the piston rod retracted by the aspiration device;
FIG. 5 shows the aspiration device in section along the line V-V in FIG. 3, and to an enlarged scale;
FIG. 6 shows the aspiration device in section along the line VI-VI in FIG. 4, and to an enlarged scale;
FIG. 7 shows the head of an injection syringe, similar to that shown in FIG. 3, but having an aspiration device shown in its normal working position of another version in accordance with the invention;
FIG. 8 shows the hypodermic syringe shown in FIG. 7 during aspiration;
FIG. 9 shows the head of a third version of hypodermic syringe in accordance with the invention, similar to that shown in FIGS. 3 and 7 and having an aspiration device in its normal working position;
FIG. 10 shows a section along line XX in FIG. 9;
FIG. 1 1 shows a side view of a fourth version of a hypodermic syringe in accordance with the invention, having an aspiration device in its normal working position, and
FIG. 12 shows a longitudinal section through the hypodermic syringe shown in FIG. 11 along the line XIXI therein.
The version of hypodermic syringe shown in FIGS. 1 and 2, is of the kind to be loaded with cylindrical ampoules. The parts of the syringe located below the line 6-6, including the piston rod and the hand grip, are known. The syringe comprises a housing 8 provided with an aperture 12 extending longitudinally thereof and intended for inserting and removing the cylindrical ampoule 10.
A removable holder 14 for the injection needle 16 is screwed on to the lower end of the syringe housing 8. The uppwer end of the syringe housing contains a bellshaped holder 18 for the cylindrical ampoule 10. The holder 18 is axially movable and is urged downwardly as viewed in FIG. 2 by a spring 20. A piston rod guide 22 in which the axially movable piston rod 24 is located engages in the upper end of the syringe housing 8. The piston rod 24 carries at its lower end a stop piece 26 which in turn carries a screwed shoulder 28. The piston rod guide 22 also serves as a holder for a finger grip piece 30 which is clamped by a threaded bush 32 screwed on to the outside of the syringe housing 8.
In order to prepare the syringe juste described for an injection, the piston rod 24 is withdrawn by means of the hand grip 34; and at the same time the bell-shaped holder 18 is withdrawn over the shoulder 26. A cylindrical ampoule can then be inserted through the side opening into the syringe housing and axially fixed and centred in the housing by releasing the hand grip 34. By turning the hand grip 34 and the piston rod 24, the screwed shoulder 28 of the piston rod is then screwed into a tapped bore in the closing piston 33 of the cylindrical ampoule. Aspiration can then be effected by pulling the hand grip 34 and injection follows on depressing the hand grip.
The aspiration device 36 in accordance with the invention is located above the finger grip piece 30 and is now described in detail with particular reference to FIGS. 5 and 6.
The piston rod guide 22 is provided with an external thread 37 above the stop for the finger grip piece, on
end of the syringe. A number of clutch balls 52 pressure-loaded through a washer 54 from a resilient element 56 are spaced around the periphery of the piston rod 24 in the bore 48. The bottom diameter of the bore 48 is smaller than the diameter of the piston rod 24 plus twice the diameter of each clutch ball 52. The piston rod guide 22 has at its upper end an annular shoulder 58 having an outside diameter which is smaller than the bottom diameter of the bore 48 of the slide 40. This annular shoulder can therefore enter the bore 48.
Te aspiration device also comprises the operating lever 60 attached to the pot-shaped housing 38 in such a way that the lever 60 can swivel and engage the slide whereby the slide can be moved from the position shown in FIG. 5 to the position shown in FIG. 6. In the illustrated version of the design, the operating lever 60 is roughly formed in the shape of a U-strap, the ends of which are bent inwardly. These bent ends engage through two diametrically opposed slots 62 in housing 38 into the holes 64 of the slide 40. The operating lever 60 is thus connected with the slide in such a manner that it can swivel.
A plate 66 acting as a fixed abutment bearing and provided with recesses 68 is attached on the outside of the housing 38 at a radial distance from the axis of the housing. The lever rests with its limbs in these openings, while the edges of the recesses form abutment bearings between which the operating lever 60 swivels. The operating lever 60 is able to slide in the longitudinal direction of its limbs during this swivelling movement.
It would alternatively also be possible to locate the operating lever 60 at a fixed swivelling point on the housing and to provide at the slide 40 pins protruding through the openings 62 and engaging the operating lever.
The normal position of the aspiration device is that shown in FIG. 5. Here, the thrust spring 44 holds the slide 40 against the upper edge of the piston rod guide 22. The annular shoulder 58 engages into the bore 48 and presses the clutch balls 52 upwardly, as viewed in FIG. 5, against the axial force of the resilient element 56. At the same time, the operating lever 60 is tilted by the upward force of the spring 44. The piston rod 24 is freely movable axially in both direction.
When aspiration is to take place, pressure must be exerted on the grip end of the operating lever 60 in a direction away from the hand grip 34. This causes the slide 40 to be shifted upwards against the force of the spring 44. The clutch balls 52 are then released from engagement with the annular shoulder 58 and are caused to be clamped, by the resilient element 56, between the conical wall and the piston rod 24. As a result of the wedge effect which is thus caused, the forces required for withdrawing the piston rod and the ampoule piston fixed to it are transmitted to the piston rod. The aspiration volume therefore depends solely on the extent of the swing movement of the operating lever and is easily controllable.
After aspiration, the operating lever 60 is released and the slide 40 is returned to its starting position as shown in FIG. 5, under the pressure of the spring 44. The wedging effect of the clutch balls 52 is thus eliminated immediately this movement starts so that no axial forces are exerted by the aspiration device on the piston rod in the direction of the ampoule. n the last phase of the releasing movement of the lever 60, the annular shoulder 58 enters the bore 48 and presses the clutch balls 52 against the resilience of the element 56 sufficiently to provide clearance around the balls 52 between the conical walls 50 and the piston rod 24.
FIGS. 7 and 8 shows the head only of the second version of the hypodermic syringe. The clutch means of the aspiration device in thisversion of the syringe is generally the same as in the aspiration device 36 in the first version. Therefore, the same references but with the prefix 1 areused for those somponents which are the same for the first version.
The aspiration device 136 comprises a piston rod guide 122 with a finger grip piece 130 mounted on it and held by a threaded bush 132. Tepiston rod guide 122 has a pot-shaped housing 138 screwed over it in which a clutch slide similar to that of the first version is arranged coaxially with the piston rod 124 and by which a thrust spring 144 is held in its idle position. Two openings 162 facing each other are formed in side flats in the housing 138. The operating lever 164 is designed as a double lever and engages with two legs on the side past the pot-shaped housing 138. The operating lever is provided with a swivel joint having axle pins 167, each formed by the pin protruding inwards and engaging in the appropriate bore in the clutch slide. Further details are described hereinafter with reference to FIGS. 8 and 10. The lever arm of the double-arm lever 164 shown in FIGS. 7 and 8 is formed in the shape of a grip 169 in which the actual gripping piece is formed as a flat just above the finger grip piece 130. The oppositelever arm 170 extends past the outside periphery of the housing 138 and rests loosely on an abutment 172 attached to'the outside of the housing 138. In order to keep the abutment 172, the supporting face of which faces the grip piece 134 of the piston rod 124, as narrow as possible, the two legs of the, doublearm lever are interconnected at the end of the arm 170 by means of a cross stay which is not shown in the drawing.
In the position shown in FIG. 7, the aspiration device 136 is disengaged from the piston rod 124 so that the piston rod 124 can move freely in both directions. For making an injection, the syringe is gripped as in FIG. 8 in such a way that the grip piece 134 rests under the thumb while the index finger and the middle finger grip under the ends of the finger grip piece 130. After the cannula of the syringe, held in this way, has penetrated the patients tissue, the third finger which is bent under the grip end 169 of the operating lever 164 can pull the operating lever upwards as viewed in FIG. 8. At the same time, the operating lever 164 is resting with the end of its lever arm 170 on the abutment 172 so that the clutch slide is lifted over the axle pins 167 thus causing the clutch to become effective. The jacking end of the lever arm 170 shifts at the same time slightly radially inward since the pins 167 and thus the swivel joint of the operating lever 164 are guided in the parallel direction over the clutch slide. The support face at the end of the lever arm 170 is suitably bent, as shown in the drawing.
Aspiration can then be sensitively adjusted by pulling the grip end 169 of the operating lever with a greater or lesser force. Particular advantage is presented by the fact that when the operating lever is pulled with the third finger, the piston rod is relieved automatically by the reduction of pressure exerted on the hand grip 134 without creating instability of the syringe in the hand.
After aspiration, the operating lever 164 is released. The clutch slide is then moved back automatically by the spring 144 to its declutched position. At the same time, the piston rod 124 is released so that injection can follow immediately without changing the position of the syringe in the hand in any way whatsoever.
While the axle pins 167 forming the swivel joint for the operating lever in the version shown in FIG. 7 are arranged at the same place and engage the clutch slide, just as in the version shown in FIGS. 1 to 6, FIGS. 9 and 10 show a third,'different version of thesyringe. In FIGS. 9 and 10, common parts are again given the same reference numbers as in FIGS. 1 to 8 but with pre-fix With reference to FIGS. 9 and 10, the operating lever 274 is formed in the shape of a double-arm lever just as in the version shown in FIGS. 7 8. The lever 274 is arranged immediately above the finger grip piece 230 on the upper face of which a plate 276 is located. The latter is formed for example, in one piece with the piston rod. guide and it being possible, for example, to screw the finger grip piece 230 to the plate 276. A can be seen from FIG. 10, the operating lever 274 is formed in the shape of a frame which is roughly rectangular and can be made from profiled wire, the ends of this profile wire being closed together in the center of the wire and then welded together to form the grip 278.
Tenon screws 282 are screwed into the two parallel members 280, with their tenon ends 284 engaging in the bores in a lower portion of the clutch slide 240. The plate 276 serves as an abutment on which the lever arm 286, lying opposite to the grip 278, rests with a connection stay 288.
The operation of thisaspiration device is the same as that shown in FIGS. 7 and 8, so that the same explanations apply in this case. The arrangement shown. in FIGS. 9 and10 is characterised by greater simplicity than that shown in FIGS. 7 and 81. As in the case of the versions shown in FIGS. 7 and 8 the point of support of the operating lever slides towards the axis of the piston.
In a further modification, the operating lever can be connected by its ends, which is opposite to the grip,
over a fixed swivel joint with the housing. In this version of the syringe, the clutch slide can be provided with driver pins protruding to the outside which either engage in slots in the operating lever or rest on the upper face of the operating lever. In order to keep transverse forces exerted at the clutch slide as low as possible a slot or a support face can be arranged at or on the operating lever in such a way that the force exerted by the lever on the tenons at the clutch slide, with the operating lever in its central position, is exactly parallel to the axis.
The part of the syringe to be supplemented underneath the grip piece or 230 can be formed in the shape of a syringe frame for injecting cylindrical ampoules. However, it is also possible to design the syringe as a normal syringe with a fixed cylinder and with a fixed piston at the bottom end of the piston rod, with which the liquid which is to be injected is drawn from i a supply bottle or a similar receptacle.
A hypodermic syringe having an aspiration device of adifferent design is shown in FIGS. 11 and 12. The same components, or those giving the same action, are in this case again marked with the same reference numbers as in the preceding figures but with the prefix 3. In this version of syringe, the piston rod guide 322 is provided with a bush-like collar 323 which has an internal thread. The upper end, provided with an external thread, of a metal bush 325 is screwed into the bush. The bush 325 is provided with side apertures, and has at its lower end an inwardly facing flange 327 with which a needle holder 329 is held. A syringe cylinder 331 made from glass or plastics is clamped between the piston rod guide 322 and the needle holder 329 in such a way that the cylinder rests against the needle holder forming a seal at that point. The cylinder 331 contains a ground piston 333 which is provided with a threaded bore into which the piston rod 324 is screwed, the latter carrying the grip piece 334 at its outer end. The piston rod guide 322 is formed with a peripheral flange 319 engaged underneath by a grip piece 330. A flange 337 at the lower end of the pot-shaped housing 338 rests on top of the flange 319. The pot-shaped housing 338 and the finger grip piece 330are connected with the flange 319 of the piston rod guide 322 by means of screws 339. The clutch slide 340 is axially movable in the potshaped housing 338 and has a conical bore 350 extending from the bottom end of the slide and widening upwards. This bore contains clutch balls 352 which, when released, as shown in FIG. 12, rest on an annular shoulder 358 of the piston rod guide 322. The balls 352 engage underneath a tube 354 which extends through the slide and on which one end of a helical spring 359 is supported. The other end of the spring 359 is supported under a ring 361 against the outer end 346 of the potshaped housing 338. A spring 344, coaxial with the spring 359, is supported with one end against the slide 340 and the other against the end 346 of the potshaped housing 338. The clutch slide 340 is provided with diametrically opposite bores 341 in which the operating lever 374 designed as a double-arm lever can swivel, just as in the versions shown in FIGS. 7 to 10. Just as in the version shown in FIGS. 9 and 10, this operating lever 374 is suitably formed as a rectangular frame which can be produced from profiled wire, the ends of this profiled wire being closed together at the centre of the wire and riveted or screwed together thus forming a grip 378. Tenon screws 382 are screwed into the two parallel members 380 of the operating lever 374, engaging with their tenon ends 384 in bores 341 of clutch slide 340. The flange 337 of this version serves also as the abutment bearing for the operating lever 374 on which the operating lever is supported by its arm opposite to the grip-378, again preferably by a connection stay 388. The operation of the version of hypodermic syringe shown in FIGS. 11 and 12 is similar to those shown in FIGS. 7 to 10.
In order to perform an injection, with any one of the foregoing versions of syringe having an aspiration device in accordance with the invention, the syringe is taken in the hand and the point of the cannula is inserted into the tissue. To perform the subsequent checking aspiration, the piston rod is retracted through the clutch of the aspiration device with the aid of the operating lever, presure on the piston rod being simultaneously stopped. At the same time, the operating lever is pushed away from the grip of the piston rod as in the version of the design shown in FIGS. 1 to 6, or pulled to the grip end of the piston rod, as in FIGS. 7 to 12, the latter versions of the syringe providing the advantage of steadier handling. If aspiration shows that the correct tissue has been entered, injection can be made immediately after releasing the operating lever. If the aspiration check is negative, the penetration depth can be corrected at the-same entry point or another puncture, followed by checking aspiration, can be made at another point.
It frequently happens, in particular in dentistry that injections at various points are made with the same ampoule contents. The aspiration device in accordance with the invention makes it possible to make the necessary aspiration check on each penetration and independently of the position of the piston rod.
What I claim as my invention and desire to secure by Letters Patent of the United States is:
l. A hypodermic syringe having an aspiration device, the syringe including a housing with finger grip means attached thereto, a piston rod slidably positioned in said housing and extending therefrom, a hand grip attached to the extending end of the piston rod and means on one end of the said housing for attaching a hypodermic needle, and the aspiration device comprising a second housing connected to the other end of said syringe housing and slidably receiving the extending portion of said piston rod, a slide member within said second housing which is slidable coaxially with the piston, an operating lever connected to said slide member, said slide member responsive to movement of said lever, a spring for returning the slide member to an initial position after releasing the operating lever and a clutch provided between the slide member and the piston rod and operable by the slide member to engage the slide member with the piston rod, whereby the piston rod is moved in response to movement of the operating lever for the purpose of aspiration. v
2. A syringe as claimed in claim 1 in which the slide member has a frusto-conical bore widening towards the end of the piston rod to be gripped by the user, the clutch including a plurality of balls acting as clutch elements and positioned in an annular space between the frusto-conical bore of the slide and the piston rod, said balls being urged to grip the piston rod by wedging action of the frusto-conical bore pursuant to axial movement fo the slide in a direction to reduce the radial clearance between the bore and the piston rod, and a stop member which extends into the conical bore when the slide member has been moved to its initial position and by which the balls are held free from engagement between the piston rod and the frustor-conical bore, said stop member forming a support for said balls.
3. A syringe as claimed in claim 2 in which the slide member is movable in a housing, the housing being provided with diametrically-opposite slots extending axially of the housing and through which the operating lever is connected to the slide member.
4. A syringe as claimed in claim 3 further comprising resilient means for urging the balls into engagement with the stop member.
5. A syringe as claimed in claim 4, said resilient means comprising an axially compressible resilient ring provided in the housing around the piston rod and engageable between the balls and the slide member.
6. A syringe as claimed in claim 3 in which stub shafts are provided on the operating lever, the stub shafts extending in opposite directions to each other through the slots in the housing into blind holes in the slide member.
7. A syringe as claimed in claim 6 in which a fulcrum for the operating lever is provided by a plate defining a fixed abutment spaced from the axis of the stub shafts and against which the lever can be swivelled.
8. A syringe as claimed in claim 7 in which the plate defining the fixed abutment is positioned between the stub shafts and the end of the operating lever to be gripped by the user.
9. A syringe as claimed in claim3 in which the operating lever comprises two arms in the form of a fork, the end of the arms remote from the end which is to be gripped by the user being engageable with a fixed abutment.
10. A syringe as claimed in claim 9 in which said fixed abutment is a flat surface provided on the outside of the housing.
11. A syringe as claimed in claim 3 in which the operating lever is formed in the shape of a substantially rectangular frame surrounding the housing.
12. A syringe as claimed in claim 3 in which the operating lever is pivotally mounted on the housing at the end thereof remote from the end which is to be gripped by the user, the slide member including pins projecting through the slots in the housing and being engageable with the lever in such a way that the clutch will be engaged when the lever is pulled towards the end of the piston rod that is to be gripped by the user.
13. A syringe as claimed in claim 2 in which movement of the slide member to its initial position by the return spring releases the clutch to disconnect the slide member from the piston rod.
14. A syringe as claimed in claim 13 in which the return spring for the slide member is a compression spring co-axially mounted on the piston rod and acting between the housing and the slide member.
15. A syringe as claimed in claim 2 including a pair of fixed stops between which the slide member is movable.
16. A syringe as claimed in claim 4, said resilient means comprising a second spring positioned co-axially within the slide-returning spring.