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20. Coincidences between the epizootic and epidemic.

21. The precedence of the epizootic.

22. The necessary Intermediary between the epizootic and the epidemic. 23. The occasional systematic examination of rats in sea-port cities.

24. The Influence of fumigation and disinfection on plague infected rats. 25. The question of Railways and Rats.

26. The question of general epizootic plague from rat plague.

So far as we know the rat is the most susceptible animal to plague infection. All species of rats appear equally susceptible. Hence the widespread occurrence of spontaneous infection amongst this species of rodents. The disease may occur in various types in these animals.

Acute plague infection would appear to be the most frequent type of the disease met with. Chronic infection is also prevalent and its presence is of im- portance epidemiologically.

There is good reason to believe in the prevalence of latent infection in rats. This would appear to have much to do with the continued prevalence of infection amongst rats, and with chronic rat plague, to have considerable importance in regard to the bridging over of plague epidemics.

Acute Rat Plague, Symptomatology.—The rat may become infected with plague through many channels. According to the method of incorporation of the plague virus, the animal suffers. Sooner or later the inoculated animal becomes dull and refuses to move actively about its cage. It crouches and if left alone usually takes up a slouching position in one of the corners of its cage. The animal sits in a curled up posture, emitting from time to time short sharp squeals. There is complete loss of appetite, ruffling of the hair, mucous discharge from the mouth, diarrhea, and a distinct rise in temperature. Handling of the animal would appear to produce pain. The abdomen is extremely tender to touch. Occasional twitching of the muscles of the extremities are observed. The reflexes are decidedly exaggerated. For a day or two previous to death. the animal appears unable to move, irregular convulsive seizures take place, and the urine and fœces are voided with each acute tonic spasm. Before death. the animal would appear to be in great pain. It falls on one side, breathes convulsively, is absolutely helpless, becomes gradually comatose, and dies as the result of a convulsive seizure. Death usually occurs in from three to five days.

The

Post-mortem Appearances of Acute Rat Plague. The subcutaneous tissues are congested and show scattered and varying size I hæ norrhagic extravasations. superficial lymphatic glands are enlarged, slightly edematous, congested on section with occasional corticel hæmorrhage.

In certain instances, distinct superficial bubonic formation may be found.

If the animal has been inoculated through the skin, one finds around the point of inoculation, considerable swelling. edema, and infiltration of the connective tissue with blood.

The general appearance presented by the internal organs, is that of vascular injection. The blood itself is dark in colour and fluid. The myocardium is in a condition of granular degeneration. The lungs are full of dark coloured, thick, blood, and frequently one finds apoplectic looking patches of consolidated tissue on section of the visci. The liver, spleen, and kidneys, in addition to congestion, frequently contain small areas of necrosis. These resemble necrotic patches found in the liver in cases of typhoid fever.

The

The peritoneal cavity usually contains an excess of blood stained fluid. peritoneum is smooth and shiny. No inflammation is found. Small retro peri- toneal hæniorrhages are often found. The mesenteric lymphatic glands are usually enlarged and congested. Occasionally extensive hemorrhages have been found between the layers of the mesentery, embe Iding enlarged, and hæmorrhagic looking lymphatic glands. The walls of the internal gut are thickened, soft and oedema- tous. Erosions and petechial hæmorrhages are found in the nucous membrane. The contents of the intestine are often deeply stained with altered blood pigment.