2. Cultivating in suitable media, but at an unsuitable temperature.

3. Cultivating in suitable media, but in an unsuitable atmosphere.

4. Cultivation in suitable media, but under unfavorable conditions as to light, motion, etc.

5. By a combination of two or more of the above methods.

XVI. POST-MORTEM EXAMINATIONS

OF EXPERIMENTAL ANIMALS.

THE post-mortem examination should be carried out as soon as possible after the death of the animal, for it must be remembered that even in cold weather the tissues are rapidly invaded by numerous bacteria derived from the alimentary tract or the cavities of the body, and from external sources.

The following outlines refer to a complete and exhaustive necropsy, and in routine work the examination will rarely need to be carried out in its entirety. In all examinations, however, the searing irons must be freely employed, and it must be recollected that one instrument is only to be employed to seize or cut one structure. This done, it must be regarded as contaminated and a fresh instrument taken for the next step.

Scalpels.

Spear-headed platinum spatula (Fig. 156).

Searing irons (Fig. 154).

Platinum loop.

Tubes of media-bouillon and oblique agar.

Grease pencil.

Sterile capillary pipettes.

Sterile capsules.

Cover-slips.

Bottles of fixing fluid (for pieces of tissue intended for sectioning).

1. Place the various instruments, forceps, scissors, scalpels, etc., needed for the autopsy inside the steriliser and sterilise by boiling for ten minutes; then raise

the tray from the steriliser, close the lid of the latter, and rest the tray on it.

2. Heat the searing irons to redness in a separate gas

stove.

3. Fasten the body of the animal, ventral surface upwards (unless there is some special reason for having

Fig. 154. Searing iron.

the dorsum exposed), out on a board by means of copper nails driven through the extremities.

4. Drench the fur (or feathers) with lysol solution, 2 per cent. This serves the twofold purpose of preventing the hairs from flying about and entering the body cavities during the autopsy, and of rendering innocuous any vermin that may be present on the animal.

Fig. 155.-Apparatus for post-mortem examination, animal on board.

5. With sterile forceps and scalpel incise the skin in the middle line from the top of the sternum to the pubes. Make other incisions at right angles to the first out to the axillæ and groins, and reflect the skin in two lateral flaps. (Place the now infected instruments on the board by the side of the body or support them on a porcelain knife rest.)

6. Inspect the seat of inoculation. If any local lesion is visible, sear its exposed surface and remove material to make cultivations and cover-slip preparations from the deeper parts by means of the platinum loop. Collect specimens of pus or other exudation in capillary pipettes for subsequent examination.

7. Sear the whole of the exposed surface of the thorax with the searing irons.

8. Divide the ribs on either side of the sternum and remove a rectangular portion of the anterior chest wall with sterile scissors and a fresh pair of forceps, exposing the heart. Place the infected instruments by the side of the first set.

9. Raise the pericardial sac in a fresh pair of forceps and burn through this structure with a searing iron. 10. Grasp the apex of the heart in the forceps and sear the surface of the right ventricle.

II. Plunge the open point of a capillary pipette through the seared area into the ventricle and fill with blood.

Make cultivations and cover-slip preparations of the heart blood.

12. Sear a broad track in the middle line of the abdominal wall; open the peritoneal cavity by an incision in the centre of the seared line.

13. Collect a specimen of the peritoneal fluid (or pus, if present) in a capillary pipette. Make cultivations and cover-slip preparations from this situation.

14. Collect a specimen of the urine from the distended bladder in a large pipette (in the manner indicated for heart blood), for further examination, by cultivations, microscopical preparations, and chemical analysis.

15. Excise the spleen and place it in a sterile capsule. (Sear the surface of this organ; plunge the spearheaded spatula through the centre of the seared area, twist it round between the finger and thumb, and re

move it from the organ. Sufficient material will be brought away in the eye in its head to make cultivations. A repetition of the process will afford material for cover-slip preparations.)

16. In like manner examine the other organs-liver, lungs, kidneys, lymphatic glands, etc. Prepare cultivations and cover-slip preparations.

17. Examine the other cavities of the body.

18. Remove small portions of various organs and place in separate bottles of "fixing fluid" for future. sectioning. Affix to each bottle a label bearing all necessary details as to its contents.

19. If necessary, remove portions of the organs for preservation and display as museum specimens (vide page 292).

20. Gather up all the infected instruments, return

them to the steriliser, and disinfect by boiling for ten minutes.

21. Cover the exposed cavities of the body with blotting or filter paper, moistened with 2 per cent. lysol solution.

22. Cremate the cadaver together with the board. upon which it is fixed.

23. Stain the cover-slip preparations by suitable methods and examine microscopically.

24. Incubate the cultivations and examine carefully from day to day.

25. Make full notes of the condition of the various body cavities and of the viscera immediately the autopsy is completed; and add the result of the microscopical and cultural investigation when available.

26. Finally, the results of the action of the organism