GB1594505A - Multi-dose jet injection device powered by foot operated pump - Google Patents

Description

(54) MULTI-DOSE JET INJECTION DEVICE POWERED BY FOOT OPERATED PUMP (71) We, VERNITRON CORPORA TION, a corporation of the State of Delaware, United States of America, of 175 Community Drive, Great Neck, New York 11024, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to medical inoculation injection instruments and more particularly to high speed multidose hypodermic jet injection instruments.

The present invention involves improvements over the hypodermic jet injection device described in U.K. Patent 959,397. In the prior injection device, two operating triggers are provided. One trigger serves to cock the device arming it for ejection of a medicament. The other trigger serves to fire the device, i.e. to eject the fluid medicament from the barriel of the device. Hydraulic power for energizing the device is obtained from a remotely located tank containing a liquid under pressure.

It is a principal object of the present invention to provide further improvements over prior methods of effecting innoculation by means of a thin high pressure stream or jet of vaccinating fluid, wherein multiple doses of vaccine are given to a number of patients without the need for reloading the injection instrument with a new reservoir of vaccine before each shot is administered. The present invention is particularly novel and useful in providing a jet injection instrument capable of administering inoculation shots to a very large number of patients within a very small interval of time, without any necessity for sterilization of the instrument between shots, without risk of injury or cross-infection to the patient, and with great accuracy in metering the required dosage of inoculation fluid. In use, instantaneous rates as high as 4,000 patients per hour for short periods of time have been achieved in administering a Q cc.

dose of vaccine. Usually the movement of people rather than injector capabilities limits the inoculating rate.

It is an object of the instant invention to provide a jet hypodermic injection device by which inoculations can be given to more patients in a shorter time, with much greater safety and much more economically than was formerly possible either with the conventional hypodermic needles and syringes or with other types of hypodermic injection devices.

It is another object of the instant invention to provide a hypoderimc high shooting rate, which permits the vaccine being administered to be changed from one type to another very easily, rapidly, and under sterile conditions and which permits prescribed dosages of vaccine to be altered very rapidly and accurately.

Another object of the present invention is to provide a hypodermic jet injection gun which is well balanced with a centrally disposed load, which can be operated and comfortably held by the operator in one hand, leaving the operator's other hand free to swab or grasp the patient, which is relatively noiseless and free from recoil, and which lends itself to long periods of fatigue-free operation.

The latter characteristic of this invention is extremely important when inoculations are being administered by a high speed jet injection, since if the gun is permitted to slip on the arm of a patient when it is fired, a nasty cut may result. Eliminating the locking trigger and associated valves from the prior injector permits the contruction of a smaller, lighter, more comfortable grip which enhances operator comfort.

Another object of the present invention is to provide a hypodermic jet injection device which can be quickly and easily disassembled, which can be easily and efficiently sterilized by autoclavin or other means, and which can be readily serviced by using conventional hand tools without the need for specially adapted tools or devices.

Another object of the present inevntion is to provide a hydraulic jet injection gun so constructed that a failure in any one portion of the gun will be isolated to that portion and so constructed that there is a path to the exterior of the gun near each seal in the mechanism. The latter feature insures that if any one of the seals should fail, fluid (either inoculating fluid or hydraulic fluid) will appear at the surface of the gun adjacent to the seal and enable the operator to immediately discern which of the several seals has failed or is leaking.

Another object of the present invention is to provide a hypodermic jet injection device ideal for use in isolated areas, where it is difficult to obtain spare or replacement parts, or which requires no external power source, is relatively trouble-free, and is easy to keep in operating condition.

With the device of the instant invention only the inoculating fluid goes below the skin level of the patient, and it is relatively easy to insure sterile operating conditions; whereas with conventional hypodermic injection devices part of the device itself penetrates beneath the skin and necessitates the most stringent requirements for sterility in the older devices.

The present invention provides a hypodermic jet injection device, which requires no sterilization either between shots or even when the type of vaccine is changed, which delivers accurately measured doses of vaccine once it is pre-set which is not dependent upon the operator to control accuracy of the dose as conventional devices are, and which creates no danger of cross-infection, since nothing but the inoculating fluid itself penetrates beneath the skin of the patient. The latter characteristic is especially helpful in preventing the spread of infectious hepatitis, and the danger of spreading hepatitis infection is an outstanding disadvantage of the older method of administering inoculations by the use of syringes and hypodermic needles. It is possible for a patient to be a carrier of hepatitis and capable of seriously infecting another patient with the disease, although the carrier himself may show none of the symptoms associated with hepatitis. One of the outstanding benefits conferred by the invention in helping to prevent hepatitis or other cross-infection, is that if operation of the jet injection device is commenced with the device in a sterile condition, the gun will maintain its own sterility.

It is a further object of the instant invention to provide a hypodermic jet injection gun which is of an inestimable value for use under emergency or epidemic conditions when it is essential that a great many shots be administered in the shortest possible time with a maximum amount of safety. The efficiency of design and simplicity of operation of the invention obviate the need for a skillful operator. Almost any intelligent person can satisfactorily operate the gun after a rudimentary amount of training.

According to the invention there is provided a hydraulic-powered jet injection instrument comprising: a body with a hydraulic chamber and an inoculating fluid chamber; a source of inoculating fluid connected to a forward position of said inoculating fluid chamber; a hydraulic piston reciprocally mounted in said hydraulic chamber; a spring for biasing said hydraulic piston into a forward position in said hydraulic chamber; an inoculating fluid plunger reciprocally mounted in said inoculating fluid chamber; means defining an ejection orifice connected to a forward position of said inoculating fluid chamber; mechanical means connecting said inoculating fluid piston to said hydraulic piston so that said inoculating fluid piston moves in response to movement of said hydraulic piston; a foot operated hydraulic pump constituting a source of hydraulic fluid under pressure; a first conduit providing an unobstructed forward path for flow of said hydraulic fluid directly from said pump and through a portion of said body to said forward position of said hydraulic chamber, whereby flow of said hydraulic fluid in said first conduit will move said hydraulic piston to a rear position in said hydraulic chamber and compress said spring and simultaneously move said inoculating fluid plunger to a rear position in said inoculating fluid chamber thereby permitting inoculating fluid from said source to enter said inoculating chamber; a second conduit providing a return path for flow of said hydraulic fluid from said forward position of said hydraulic chamber through a portion of said body to said pump; a check valve in said hydraulic pump connected to said first conduit, preventing return of said hydraulic fluid from said hydraulic chamber through said first conduit to said pump; and a valve trigger in said body connected to said second conduit which when actuated permits said hydraulic fluid to flow from said hydraulic chamber to said pump whereby said spring drives said hydraulic piston and said inoculating plunger to a forward position in said respective chamber and causes said inoculating fluid to be ejected from said inoculating chamber, through said ejection orifice.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a central vertical sectional view of the hypodermic jet injection device, with associated foot operated hydraulic pump shown in side elevation.

Figure 2 is a horizontal sectional view through the foot operated hydraulic pump, taken on line 2-2 of Figure 1.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout, there is illustrated in Figure 1 a hypodermic jet injection device having a hydraulic chamber 10, a hydraulic piston 12, a spring chamber 14, a compression spring 16, and a spring guide 18. The device includes a main body 19 which in turn comprises a barrel 20 and a grip 21 and the hydraulic chamber 10 and the spring chamber 14 are formed in the barrel 20. The spring chamber 11 of the barrel 20 is closed with a square cap 22 to which a dosage adjusting screw 24 is threadedly engaged. At its interior end the dosage adjusting screw 24 is provided with a thrust ball bearing 26 which bears against one end of the spring -16. The dosage adjusting screw 24 has an adjusting knob 28 secured to its exterior end to permit hand operation of the screw. At one end the spring 16 bears against the thrust ball bearing 26 and at the other end bears against the hydraulic piston 12 so that the spring may be adjustably compressed between these two bearing surfaces (thrust bearing 26 and hydraulic piston 12) by turning the dosage adjusting screw 24.

As embodied, the hydraulic piston 12 includes a plunger 30 which reciprocates in a cylinder 31 formed in the forward end of the barrel 20. Also as embodied, the means to meter vaccine comprises a vaccine pump cylinder 33 formed by a barrel extension 32 which is attached to the barrel 20 by a threaded barrel extension cap 34. A vaccine pump piston 36 is secured to the hydraulic piston plunger 30 at the forward end of the plunger and the vaccine piston 36 reciprocates in the vaccine pump cylinder 33 responsive to movement of the hydraulic piston 12. Included in the vaccine pump piston 36 is a groove, not shown, in which appropriate sealing rings may be mounted to seal the forward portion, or vaccine chamber 39, of the vaccine pump cylinder 33 from the rear of the cylinder.

The forward portion of the barrel extension 32 is adapted to receive a closure member 40, and the closure member 40 is held firmly in place at the end of the barrel extension 32 by a nozzle cap 42 which is threadedly engaged to the exterior of the barrel extension 32.

A vaccine inlet valve 48 is carried by a member 50 which is secured to the top of the barrel extension 32, and a vaccine inlet tube 52 leads from the vaccine inlet valve 48 to a vaccine chamber 39 in the barrel extension 32. A vaccine extracting tube 54 is wedged on the tapered nose of the vaccine inlet valve 48 and secured thereto by conventional means. The tube 54 includes a right angle bend so that its rear portion extends in a vertical direction when the device or gun is in firing position.

Within the upright portion of the vaccine extracting tube 54 is an air vent tube 55 of smaller diameter but concentric with the vaccine extracting tube 54. The vaccine extracting tube 54 includes a longitudinal port 56 by means of which vaccine is withdrawn from a conventional vaccine bottle 58 and into the tube 54.

The air vent tube 55 is provided with an air filter 60 which in use would be filled with sterile cotton to trap any impurities which might otherwise be drawn into the vaccine bottle 58 along with outside air as vaccine its withdrawn from the bottle.

A clip 62 is secured to the barrel 20. On top and centrally disposed on the clip 62 is a U-shaped tube support 64 whcih is welded or otherwise secured to the clip 62. The vaccine extracting tube 54 is held by the Ushaped tube support 64 and the support 64 is provided with two small stops 66 which come to rest against the upright portion of the tube 54 and determine the position of the clip 62 on the barrel of the gun stock 20.

The U-shaped tube support 64 also acts as a positive stop for the vaccine bottle 58 when the bottle is pushed onto the upright portion of the tube 54 to provide the vaccine supply for operation of the gun.

The U-shaped tube support 64 secures the vaccine extracting tube 54 against horizontal movement and a spring loaded retractable vaccine extracting lock 68 secures the needle tube 54 against vertical movement. The lock 68 and the tube support 64 thus co-operate to hold the tube 54 in a rigid, upright, and easily accessible position and at the same time prevent the relatively delicate vaccine extracting tube 54 from being easily dislodged and bent or otherwise damaged. The tube support 64 also acts as a channel to secure the air vent tube 55 against horizontal movement and the stops 66 in the support 64 help to secure the air vent tube from vertical movement.

In use, the air vent tube 55 acts to admit air to the vaccine bottle 58 as vaccine is withdrawn and prevents the formation of a vaccum within the bottle.

The means to control the accumulation and release of force comprises a foot operated hydraulic pump generally designated as reference numeral 100,. the firing mechanism and the conduits and valves which control application of hydraulic power to the gun. These elements are associated with the grip 21 or are inside the grip 21. The gun is provided with a single firing trigger 76.

Pump 100 is similar to the pump described in U.S. Patent 3,301,190. The pump includes a rigid housing 102 at one end of which is pivotally mounted a foot pedal 104. The pedal 104 pivots on a shaft 106 and moves a piston 108 in a chamber 110 axially to the right; see Fig. 2. This drives hydraulic fluid 112 out of the chamber 110. The pressurized fluid opens a spring loaded discharge valve 114 in a passage 116. The hydraulic fluid leaves the pump 100 via a fitting 118 and flows through a hose 120 to coupling fitting 122 at the outer end of an inlet conduit 87 in the hand grip 21. The pressurized fluid enters the hydraulic chamber 10 and causes the piston 12 to retract thereby compressing the spring 16. The fluid is prevented from leaving the chamber 10 by the discharge valve 114 in the pump 100, and by a check valve 86 in the injector.

When the firing trigger 76 is depressed it actuates a trigger pin 84 which in turn opens a spring loaded ball check valve 86 permitting rapid escape of the hydraulic fluid from the chamber 10. The release of hydraulic fluid from the chamber 10 permits the spring 16 acting through intermediate parts to drive the vaccine piston 36 forward into the vaccine chamber 39 with great speed and force. The fluid expelled from the hydraulic fluid chamber 10 passes through an outlet conduit 89 in the grip 21 and through a coupling fitting 124 to a hose 125. The hose 125 is connected to a fitting 126 at the pump 100. The fluid enters a reception chamber 128 (Fig. 2) and fills it even though the pedal 104 is not released.

When the pedal 104 is released fluid passes from the reception chamber 128 through the check valve 130 to refill the chamber 110.

When the piston 12 is pushed to the rear of the gun by hydraulic fluid during the cocking operation, it acts through intermediate parts to move the vaccine pump piston 36 toward the rear an equal distance. The movement of the vaccine piston 36 to the rear tends to create a vacuum within the vaccine chamber 39 and causes vaccine to be drawn into the chamber 39 in an amount pre-deter-.

mined by the distance through which the vaccine piston 36 is set to move. The vaccine is withdawn from the bottle 58 through the port 56 into and through the vaccine extracting tube 54 beyond the vaccine inlet valve 48 and through the vaccine inlet tube 52 into the vaccine chamber 39.

Side port 56 is employed in the vaccine extracting tube 54 to prevent rubber from the vaccine stopper from entering the needle tube when the stopper is pierced. The side port 56 also provides a change in direction in the vaccine flow path which aids in preventing foreign particles from being entrained with the vaccine entering the pump and clogging an outlet valve (not shown), the inlet valve 48 or an exit orifice, not shown. The concentric air vent tube 55 yields a stronger structure for the needle assembly and minimizes the size of the hole which must be made in the vaccine stopper thereby effecting a better seal between stopper and tube and minimizing the tearing off of particles or rubber. This characteristic is important in helping to insure trouble-free operation, since it is not uncommon for pieces or rubber stopper to be broken off when the needle end of the tube assembly is inserted into the vaccine bottle.

With the gun cocked, when the operator depresses the trigger 76, it acts through the firing pin 84 to open the check valve 86, and the hydraulic fluid locked in the chamber 10 is given free path back to hydraulic pump 100. The release of hydraulic fluid pressure from the piston 12 permits the spring 16, acting through intermediate parts, to drive the vaccine pump piston 36 forward with tremendous force and speed. The forward movement of the vaccine pump piston 36 causes the vaccine or inoculating fluid in the chamber 39 to pass through a check valve (not shown) and be ejected from the front of the gun through a jeweled orifice (not shown) in a small diameter jet.

The conduits and passageway in the gun are constructed so as to offer a sufficient resistance to provide hydraulic damping to the forward movement of the piston 12. This damping is in addition to the damping normally attained due to the resistance encountered by the vaccine as it is forced through the jet orifice. This additional damping permits the unit to be dry fired (no vaccine in the vaccine pump) with no mechanical damage occuring to any portion of the injection unit. This feature assures that there will be no break in service if the operator accidentally does not renew the vaccine supply after the vaccine bottle in use has been emptied. Even if air does enter into the vaccine pump, under these conditions an injection would be impossible because there is not enough pressure generated in the pump to administer an injection.

A flat front surface 90 of the nozzle 42 is mechanically knurled to provide a roughened non-slip surface. This surface has been found of great help in practice to prevent the ejection tip of the gun from slipping or sliding on the skin surface of a patient when an ejection is being made. Without such means to prevent slippage, perspiration on the skin surface makes the gun particularly susceptible to slippage, and if the gun slips when it is being fired a severe cut can result from the knife-like action of the high pressure jet of fluid.

The vaccine inlet valve 48 and its supporting member 50 are mounted somewhat toward the rear of the gun. This arrangement keeps the shooting end of the gun clear and uncluttered so that the operator has an unobstructed view of the shooting end as it is placed in contact with the skin of the patient.

The vaccine pump is self-priming, which is an advantageous feature of the invention in practice. After loading a new bottle of vaccine onto the device, the operator may purge the vaccine pump of air and place it in condition to fire an injection by merely shooting it into the air twice.

Another advantageous feature of the present embodiment is that the ball of the vaccine inlet valve 48 floats in the valve chamber and is free to rotate. On the feed or inlet cycle of the vaccine pump, the ball permits the free flow of vaccine into the vaccine feed tube through a series of slots 53 at the rear end of the tube. When the gun is fired, however, the pressure created in the vaccine chamber 39 transmitted through the feed tube 52 forces the ball of the inlet valve 48 tightly against its seat in the valve chamber and prevents any backflow of fluid through the vaccine extracting tube 54. The seat of the valve 48 is designed so that a substantial surface of the ball is in contact with the seat when the valve is acting as a check; this reduces wear on the ball itself to a minimum. Accordingly, the latter feature and the design which permits the ball to rotate freely between cycles of the vaccine pump insure a long life for the valve in spite of its small size valve and subjection to tremendous pressure every time the gun is fired.

In operation, the operator controls the dosage of vaccine to be administered by turning the dosage adjusting screw 24 through the knob 28. When a large dose is desired the adjusting screw 24 is moved towards the rear of the gun, and when a smaller dose is desired, the screw is moved toward the front of the gun. As the screw 24 is moved toward the front of the gun, it places the spring 16 under partial compression. A pressure relief valve (not shown) in the hydraulic foot pump is set to operate after the spring 16 is fully compressed. Further pumping of the foot pedal will not increase the pressure above the valve but excess hydraulic fluid is internally shunted within the pump from a chamber 110 to the reception chamber 128 and not delivered to the injector. If the dosage adjusting screw has already partially compressed the spring 16, it is obvious that the vaccine pump piston 36 will only move as far to the rear of the gun under hydraulic fluid pressure as is necessary to complete compression of the spring 16.

Accordingly, the degree to which the vacuum pump piston 36 moves to the rear can be directly controlled by the dosage adjusting screw 24, and the degree to which the piston move to the rear obviously determines the amount of vaccine drawn into the vaccine pump chamber 39 and in the amount which is ejected upon firing.

In practice, the extent to which the spring 16 is finally compressed is determined by the magnitude of the hydraulic fluid pressure, which in turn, is controlled by the pressure relief valve (not shown) in the hydraulic fluid pump 100. Regardless of dosage to be administered, the spring 16 is compressed to the same degree each time the gun is cocked.

This characteristic insures that the vaccine ejection force will always be the same at the instant the firing trigger is depressed, no matter what volume dose is being administered.

Screwing in the dosage adjusting screw 24 merely pre-compresses the firing spring 16 mechanically so that the hydraulic fluid will only be required to further compress the spring a short distance before the gun is fully cocked. If the dosage adjusting screw is turned in all the way, only a very slight further compression of the spring is possible, and in the present embodiment, the vaccine piston 36 can only move back the equivalent of 0.1 cc.

of vaccine dose. Conversely, if the dosage adjusting screw is turned out all the way, the spring must be compressed through its fully acting distance by the hydraulic system, and in the present embodiment, a 1.0 cc. dose will be administered. The rear surface 23 of the guide spring guide 18 strikes the internal face of the dosage adjustment knob 28 to limit the maximum compression of the firing spring 16 when it is being driven rearward by hydraulic pressure or forward by the dosage adjustment knob. This arrangement keeps the maximum spring compression below that which would cause spring damage and at a constant maximum amount of compression regardless of dosage setting.

Of course, the characteristic last described is an important advantage of the present embodiment, since it guarantees that regardless of the size of the dose, the injection force at the start of the firing stroke is always the same and imparts to the jet of inoculating fluid the correct speed and pressure for insuring an effective hypodermic injection.

WHAT WE CLAIM IS:- 1. A hydraulic-powered hypodermic jet injection instrument comprising: a body with a hydraulic chamber and an inoculating fluid chamber; a source of inoculating fluid connected to a forward portion of said inoculating fluid chamber; a hydraulic piston reciprocally mounted in said hydraulic chamber; a spring for biasing said hydraulic piston into a forward position in said hydraulic chamber; an inoculating fluid plunger reciprocally mounted in said inoculating fluid chamber; means defining an ejection orifice connected to a forward position of said inoculating fluid chamber; mechanical means connecting said inoculating fluid piston to said hydraulic piston so that said inoculating fluid piston moves in response to movement of said hydraulic piston;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   vaccine pump of air and place it in condition to fire an injection by merely shooting it into the air twice.

   Another advantageous feature of the present embodiment is that the ball of the vaccine inlet valve 48 floats in the valve chamber and is free to rotate. On the feed or inlet cycle of the vaccine pump, the ball permits the free flow of vaccine into the vaccine feed tube through a series of slots 53 at the rear end of the tube. When the gun is fired, however, the pressure created in the vaccine chamber 39 transmitted through the feed tube 52 forces the ball of the inlet valve 48 tightly against its seat in the valve chamber and prevents any backflow of fluid through the vaccine extracting tube 54. The seat of the valve 48 is designed so that a substantial surface of the ball is in contact with the seat when the valve is acting as a check; this reduces wear on the ball itself to a minimum. Accordingly, the latter feature and the design which permits the ball to rotate freely between cycles of the vaccine pump insure a long life for the valve in spite of its small size valve and subjection to tremendous pressure every time the gun is fired.

   In operation, the operator controls the dosage of vaccine to be administered by turning the dosage adjusting screw 24 through the knob 28. When a large dose is desired the adjusting screw 24 is moved towards the rear of the gun, and when a smaller dose is desired, the screw is moved toward the front of the gun. As the screw 24 is moved toward the front of the gun, it places the spring 16 under partial compression. A pressure relief valve (not shown) in the hydraulic foot pump is set to operate after the spring 16 is fully compressed. Further pumping of the foot pedal will not increase the pressure above the valve but excess hydraulic fluid is internally shunted within the pump from a chamber 110 to the reception chamber 128 and not delivered to the injector. If the dosage adjusting screw has already partially compressed the spring 16, it is obvious that the vaccine pump piston 36 will only move as far to the rear of the gun under hydraulic fluid pressure as is necessary to complete compression of the spring 16.

   Accordingly, the degree to which the vacuum pump piston 36 moves to the rear can be directly controlled by the dosage adjusting screw 24, and the degree to which the piston move to the rear obviously determines the amount of vaccine drawn into the vaccine pump chamber 39 and in the amount which is ejected upon firing.

   In practice, the extent to which the spring

   16 is finally compressed is determined by the magnitude of the hydraulic fluid pressure, which in turn, is controlled by the pressure relief valve (not shown) in the hydraulic fluid pump 100. Regardless of dosage to be administered, the spring 16 is compressed to the same degree each time the gun is cocked.

   This characteristic insures that the vaccine ejection force will always be the same at the instant the firing trigger is depressed, no matter what volume dose is being administered.

   Screwing in the dosage adjusting screw 24 merely pre-compresses the firing spring 16 mechanically so that the hydraulic fluid will only be required to further compress the spring a short distance before the gun is fully cocked. If the dosage adjusting screw is turned in all the way, only a very slight further compression of the spring is possible, and in the present embodiment, the vaccine piston 36 can only move back the equivalent of 0.1 cc.

   of vaccine dose. Conversely, if the dosage adjusting screw is turned out all the way, the spring must be compressed through its fully acting distance by the hydraulic system, and in the present embodiment, a 1.0 cc. dose will be administered. The rear surface 23 of the guide spring guide 18 strikes the internal face of the dosage adjustment knob 28 to limit the maximum compression of the firing spring 16 when it is being driven rearward by hydraulic pressure or forward by the dosage adjustment knob. This arrangement keeps the maximum spring compression below that which would cause spring damage and at a constant maximum amount of compression regardless of dosage setting.

   Of course, the characteristic last described is an important advantage of the present embodiment, since it guarantees that regardless of the size of the dose, the injection force at the start of the firing stroke is always the same and imparts to the jet of inoculating fluid the correct speed and pressure for insuring an effective hypodermic injection.

   WHAT WE CLAIM IS:- 1. A hydraulic-powered hypodermic jet injection instrument comprising: a body with a hydraulic chamber and an inoculating fluid chamber; a source of inoculating fluid connected to a forward portion of said inoculating fluid chamber; a hydraulic piston reciprocally mounted in said hydraulic chamber; a spring for biasing said hydraulic piston into a forward position in said hydraulic chamber; an inoculating fluid plunger reciprocally mounted in said inoculating fluid chamber; means defining an ejection orifice connected to a forward position of said inoculating fluid chamber; mechanical means connecting said inoculating fluid piston to said hydraulic piston so that said inoculating fluid piston moves in response to movement of said hydraulic piston;

   a foot operated hydraulic pump constituting a source of hydraulic fluid under pressure; a first conduit providing an unobstructed forward path for flow of said hydraulic fluid directly from said pump and through a portion of said body to said forward position of said hydraulic chamber, whereby flow of said hydraulic fluid in said first conduit will move said hydraulic piston to a rear position in said hydraulic chamber and compress said spring and simultaneously move said inoculating fluid plunger to a rear position in said inoculating fluid chamber thereby permitting inoculating fluid from said source to enter said inoculating chamber; a second conduit providing a return path for flow of said hydraulic fluid from said forward position of said hydraulic chamber through a portion of said body to said pump; a check valve in said hydraulic pump connected to said first conduit, preventing return of said hydraulic fluid from said hydraulic chamber through said first conduit to said pump; and a valve trigger in said body connected to said second conduit which when actuated permits said hydraulic fluid to flow from said hydraulic chamber to said pump whereby said spring drives said hydraulic piston and said inoculating plunger to a forward position in said respective chamber and causes said inoculating fluid to be ejected from said inoculating chamber, through said ejection orifice.
2. 2. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 1, wherein said pump comprises: a foot operated pedal; a pump body pivotally carrying said pedal and having another hydraulic chamber therein; another hydraulic piston in said other hydraulic chamber connected to said pedal for reciprocation thereby in said other hydraulic chamber; and hydraulic fluid in said other hydraulic chamber drivable out of said other hydraulic chamber and through said first conduit to the first named hydraulic chamber when said pedal is operated.
3. 3. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 2, wherein said other hydraulic chamber has an outlet opening, and further comprising a conduit in said pump body providing a path for said hydraulic fluid from said other hydraulic chamber to said first conduit, said check valve being operatively disposed in said conduit in said pump body at said outlet opening of said other hydraulic chamber.
4. 4. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 3, wherein said other hydraulic chamber has an inlet opening, and further comprising a further conduit in said pump body providing a path for said hydraulic fluid from said second con duit to said other hydraulic chamber when said hydraulic fluid is returned from said first named hydraulic chamber after said firing trigger is actuated and said foot operated pedal is released.
5. 5. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 4, further comprising a further check valve in said pump body disposed in said further conduit for controlling flow of fluid in said other hydraulic chamber and preventing flow of fluid out of said other hydraulic chamber via said further conduit.
6. 6. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 5, further comprising a spring in said other hydraulic chamber biasing said other hydraulic piston of said other hydraulic chamber to raise said foot operated pedal.
7. 7. A hydraulic-powered hypodermic jet injection instrument as defined in Claim 6, wherein said further conduit comprises a reception chamber for said fluid in said body, said second conduit opening into said reception chamber, and said reception chamber opening into said other hydraulic chamber via said further check valve.
8. 8. A hydraulic-powered hypodermic jet injection instrument substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.