The Elements of Bacteriological Technique Part 96

4. Inject the contents of the syringe slowly.

5. Label, etc.

~8. Intravenous.~--

_Fluid Inoculum._--(_Anaesthetic, none._)

The site selected for the injection in the rabbit is the posterior auricular vein (see Fig. 192). Although this is smaller than the median vein, it is firmly bound down to the cartilage of the ear by dense connective tissue, and is therefore more readily accessible. (In the guinea-pig the jugular vein must be utilised, and in order to perform the inoculation satisfactorily a general anaesthetic must be administered to the animal. In the monkey or the dog, the internal saphenous vein is the most convenient and before puncturing should be distended or rendered prominent by compressing the vein above the selected site.)

_Preparation of the Inoculum._--Care must be taken in preparing the inoculum, as the injection of even small fragments may cause fatal embolism. To obviate this risk the fluid should, if possible, be filtered through sterile filter paper before filling into the syringe.

Air bubbles, when injected into a vein, frequently cause immediate death. To prevent this, the syringe after being filled should be held in the vertical position, needle uppermost. A piece of sterile filter paper is then impaled on the needle and the piston of the syringe pressed upward until all the air is expelled from the barrel and needle. Should any drops of the inoculum be forced out, they will fall on the filter paper, which should be immediately burned.

1. Have the animal firmly held by an a.s.sistant. The selected ear is grasped at its root and stretched forward toward the operator.

2. Shave the posterior border of the dorsum of the ear.

3. Disinfect the skin over the vein, rubbing it vigourously with cotton-wool soaked in lysol. The friction will make the vein more conspicuous. Wash the lysol off with ether and allow the latter to evaporate.

4. Direct the a.s.sistant to compress the vein at the root of the ear.

This will cause its peripheral portion to swell up and increase in calibre.

5. Hold the syringe as one would a pen and thrust the point of the needle through the skin and the wall of the vein till it enters the lumen of the vein (Fig. 189). Now press it onward in the direction of the blood stream--i. e., toward the body of the animal.

6. Direct the a.s.sistant to cease compressing the root of the ear, and _slowly_ inject the inoculum. (If the fluid is being forced into the subcutaneous tissue, a condition which is at once indicated by the swelling that occurs, the injection must be stopped and another attempt made at a spot closer to the root of the ear or at some point on the corresponding vein on the opposite ear.)

7. Withdraw the needle and press a pledget of cotton-wool over the puncture to ensure closure of the aperture in the vein wall.

8. Label, etc.

[Ill.u.s.tration: FIG. 189.--Intravenous inoculation.]

~9. Inhalation.~--

(a) _Fluid Inoculum._--(_Anaesthetic, none._)

1. Place the animal in a closed metal box.

2. Through a hole in one side introduce the nozzle of some simple spraying apparatus, such as is used for nasal medicaments.

3. Fill the reservoir of the instrument (previously sterilised) with the fluid inoculum, and having attached the bellows, spray the inoculum into the interior of the box.

4. On the completion of the spraying, open the box, spray the animal thoroughly with a 10 per cent. solution of formaldehyde (to destroy any of the virus that may be adhering to fur or feathers).

5. Transfer the animal to its cage.

6. Label, etc.

7. Thoroughly disinfect the inhalation chamber.

(b) _Fluid or Powdered Inoculum._--_Anaesthetic, A. C. E._

1. Anaesthetise the animal and secure it firmly to the operating table.

[Ill.u.s.tration: FIG. 190.--Gag for rabbits.]

2. Prop open the mouth by means of some form of gag; seize the tongue with a pair of forceps and draw it forward.

The most convenient form of gag for the rabbit or cat is that shown in Fig. 190. It is simply a strip of hard wood shaped at the middle and provided with a square orifice through which a tracheal or oesophageal tube can be pa.s.sed.

3. Pa.s.s a previously sterilised gla.s.s tube (17 cm. long, 0.5 cm.

diameter, with its terminal 2 cm. slightly curved) down through the larynx into the trachea.

4. Connect the straight portion of a ~Y~-shaped piece of tubing to the upper end of the sterilised tube and couple one branch of the ~Y~ to a separatory funnel containing the fluid inoculum, or insufflator containing the powdered inoculum, and the other to a hand bellows.

5. Allow the fluid inoculum to run into the lungs by gravity, or blow in the powdered inoculum by means of a rubber-ball bellows.

6. Remove the intratracheal tube; release the animal from the table.

7. Label, etc.

As an alternative method in the case of fairly large animals, such as rabbits, etc., a sterile piece of gla.s.s tubing of suitable diameter may be pa.s.sed through the larynx down the trachea almost to its bifurcation. Fluid cultivations may then be literally poured into the lungs, or cultivations, dried and powdered, may be blown into the lung by the aid of a small hand bellows or even a teat pipette.

~10. Intragastric Inoculation.~--_Fluid or semi-fluid inoculum.

(Anaesthetic none.)_

The method of performing the operation is varied slightly according to the size of the experimental animal.

_A. Monkey, Rabbit, Guinea-pig._

1. Secure the animal to the operating table ventral surface uppermost.

2. Prop the mouth open with a gag; draw the tongue forward with forceps.

3. Sterilise a soft rubber catheter (No. 10 or 8 English scale, or No.

18 or 15 French) and lubricate it with sterile glycerine.

4. Pa.s.s it to the back of the pharynx, keeping the end in the middle line.

5. Gently a.s.sist the progress of the catheter down the oesophagus until it pa.s.ses the cardiac orifice of the stomach. Do not use any force.

6. Take up the required dose of inoculum into a sterilised pipette.

Insert the point of the pipette into the open end of the catheter and allow the fluid to run down into the stomach. Remove the pipette and drop it into a jar of lysol.

7. With another sterile pipette run one cubic centimetre of sterile saline solution through the catheter to wash out the last traces of the inoculum.

8. Withdraw the catheter.