In addition it is often naturally infected with _B. tuberculosis_, and it is a wise precaution to test animals as soon as they reach the laboratory by injecting Koch's Old Tuberculin--0.5 c.c. causing death in the tuberculous cavy within 48 hours.

The ~Monkey~ is naturally p.r.o.ne to tuberculosis, and should be injected with 1 c.c. Old Tuberculin on arrival in the laboratory. The tissues of the monkey also serve as the habitat for a Nematode worm parasitic in cattle (_Oesophagostoma inflatum_) resembling the Anchylostomum, and this parasite frequently bores through the intestinal wall, and provokes the formation of small cysts in the immediately adjacent mesentery. The presence of these cysts may give rise to considerable speculation at the post-mortem.

The ~Pigeon~ may be infected by _Haemosporidia_, and its blood show the presence of halteridia. This bird may also be the subject of a bacterial infection known as pigeon diphtheria; while the fowl may be subject to scabies and ringworm, or suffer from fowl cholera or fowl septicaemia--infections due to members of the haemorrhagic septicaemia group.

~Weighing.~--The larger animals are most conveniently weighed in a decimal scale provided with a metal cage for their reception instead of the ordinary pan (Fig. 166). Mice and rats are weighed in a modification of the letter balance, weighing to 250 grammes, which has a conical wire cage, (carefully counterpoised) subst.i.tuted for its original pan (Fig.

167).

[Ill.u.s.tration: FIG. 166.--Rabbit scales.]

~Temperature.~--To take the rectal temperature of any of the laboratory animals, the animal should be carefully and firmly held by an a.s.sistant.

Introduce the bulb of an ordinary clinical thermometer, well greased with vaseline, just within the sphincter ani. Allow it to remain in this position for a few seconds, and then push it on gently and steadily until the entire bulb and part of the stem, as far as the constriction, have pa.s.sed into the r.e.c.t.u.m. Three to five minutes later, the time varying of course with the sensibility of the thermometer used, withdraw the instrument and take the reading. The thermometers employed for recording temperature should be verified from time to time by comparison with a standard Kew certified Thermometer kept in the laboratory for that purpose.

[Ill.u.s.tration: FIG. 167.--Mouse scales]

~Cages.~--During the period which elapses between inoculation and death, or complete recovery, the experimental animals must be kept in suitable receptacles which can easily be kept clean and readily disinfected.

The _mouse_ is usually stored in a gla.s.s jar (Fig. 168) 11 cm. high and 11 cm. in diameter, closed by a wire gauze cover which is weighted with lead or fastened to the mouth of the jar by a bayonet catch. A small oblong label, 5 cm. by 2.5 cm., sand-blasted on the side of the cylinder, is a very convenient device as notes made upon this with an ordinary lead pencil show up well and only require the use of a damp cloth to remove them (Fig. 168).

The _rat_ is kept under observation in a gla.s.s jar similar, but larger, to that used for the mouse.

[Ill.u.s.tration: FIG. 168.--Mouse jar.]

[Ill.u.s.tration: FIG. 169.--Tripod.]

A layer of sawdust at the bottom of the jar absorbs any moisture and cotton-wool or paper shavings should be provided for bedding. The food should consist of bran and oats with an occasional feed of bread-and-milk sop.

The use of a metal tripod, on the platform of which are soldered two small cups for the reception of the food, inside the cage, prevents waste of food or its contamination with excreta (Fig. 169).

After use the jars and tripods are sterilised either by chemical reagents or by autoclaving.

The _rabbit_ and the _guinea-pig_ are confined in cages of suitable size, made entirely of metal (Fig. 170). The sides and top and bottom are of woven wire work; beneath the cage is a movable metal tray filled with sawdust, for the reception of the excreta. The cage as a whole is raised from the ground on short legs. The sides, etc., are generally hinged so that the cage packs up flat, for convenience of storing and also of sterilising.

The ordinary rat cage, a rectangular wire-work box, 30 cm. from front to back, 20 cm. wide, and 14 cm. high, makes an excellent cage for guinea-pigs if fitted with a shallow zinc tray, 35 cm. by 24 cm., for it to stand upon.

[Ill.u.s.tration: FIG. 170.--Metal rabbit rage.]

A plentiful supply of straw should be provided for bedding and the food should consist of fresh vegetables, cabbage leaves, carrot and turnip tops and the like for the morning meal and broken animal biscuits for the evening meal. Occasionally a little water may be placed in the cage in an earthenware dish.

The tray which receives the dejecta should be cleaned out and supplied with fresh sawdust each day, and the soiled sawdust, remains of food, etc., should be cremated.

These cages are sterilised after use either by autoclaving or spraying with formalin.

As ~animal inoculation~ is purely a surgical operation, the necessary instruments will be similar to those employed by the surgeon, and, like them, must be sterile. In the performance of the inoculation strict attention must be paid to asepsis, and suitable precautions adopted to guard against accidental contamination of the material to be introduced into the animal. In addition, the hands of the operator should be carefully disinfected.

The list of apparatus used in animal inoculations given below comprises practically everything needed for any inoculation. Needless to remark, all the apparatus will never be required for any one inoculation.

[Ill.u.s.tration: FIG. 171.--Hypodermic syringe with finger rests.]

Apparatus Required for Animal Inoculation:

1. Water steriliser (_vide_ page 33). It is also convenient to have a second water steriliser, similar but smaller (23 by 7 by 5 cm.), for the sterilisation of the syringes.

2. Injection syringe. The best form is one of the ordinary hypodermic pattern, 1 c.c. capacity graduated in twentieths of a cubic centimeter (0.05 c.c.), fitted with finger rests, but with the leather washers and the packing of the piston replaced by those made of asbestos (Fig. 171). The instrument must be easily taken to pieces, and spare parts should be kept on hand to replace accidental breakage or loss. Other useful syringes are those of 2 c.c., 5 c.c., 10 c.c., and 20 c.c. capacity. A good supply of needles must be kept on hand, both sharp-pointed and with blunt ends. To sterilise the syringe, fill it with water, loosen the packing of the piston and all the screw joints, place it in the steriliser and boil for at least five minutes. Disinfect the syringe _after use_, in a similar manner. The needles, which are exceedingly apt to rust after being boiled, should be stored in a pot of absolute alcohol when not in use.

3. Operating table.

4. Surgical instruments. Sterilise these before use by boiling, and disinfect them _after use_ by the same means.

Wipe perfectly dry immediately after the disinfection is completed.

Scissors, probe and sharp-pointed.

Dissecting forceps of various patterns.

Pressure forceps.

Retractors (small self retaining Fig. 172).

Aneurism needles, sharp and blunt.

Scalpels, } Keratomes, } with metal handles. Trephines, }

Michel's steel clips and special forceps for applying the same. These small steel clips enable the operator to easily and rapidly close skin incisions and are most satisfactory for animal operations.

Surgical needles.

Needle holder.

Soft rubber catheters, various sizes.

Gum elastic oesophageal bougies with connection to fit syringe.

[Ill.u.s.tration: FIG. 172. Small self retaining retractors.]

5. Anaesthetic.

(a) General: The safest general anaesthetic for animals is an A. C. E.

mixture, freshly prepared, containing by volume alcohol 1 part, chloroform 2 parts, ether 6 parts, and should be administered on a "cone" formed by twisting up one corner of a towel and placing a wad of cotton-wool inside it, or from a saturated cotton-wool pad packed into the bottom of a small beaker.

(b) Local:

1. Cocaine hydrochloride, 2 per cent. in adrenalin 1 per mille solution.

2. Beta-eucaine, 2 per cent. in adrenalin, 1 per mille solution.

3. Ethyl chloride jet.

6. Sterile gla.s.s capsules of various sizes.

7. Cases of sterile pipettes { 10 c.c. (in tenths of a cubic centimetre).

{ 1 c.c. (in hundredths of a cubic centimetre).