55
H.—3l
Infection among Rats. For about two years prior to 1907 such rats as could be obtained from about the wharves and lower parts of Auckland were examined at the Health Office, and any suspected ones were forwarded to the Wellington laboratory. From the Ist April till the 15th May some seventy rats had been thus examined, and during April, while on a visit to Auckland, I examined some of these specimens without finding anything resembling plague. After the two cases (K. and M.) had developed, an examination of the premises wherein they worked revealed beneath the floor of one room a dead rat which was submitted to me for examination. It was in a fairly advanced stage of decomposition. There was some glandular enlargement in the left groin, the spleen and liver were enlarged, and the lungs showed pneumonic patches. Typical bipolar-staining bacilli were found in gland, spleen, and heart-blood. These decolorised by Gram's method. Putrefactive sporulating organisms were also present. No inoculative experiments were made, but from the microscopic characters I am convincted that this rat died from plague. During the next few days as many rats as could be obtained were examined at the laboratory. In some forty of these microscopic examination w r as made, and in three, which had been sent from a small coastal steamer at Onehunga, some bacilli were found in the spleen-pulp which resembled the Bacillus pestis. Unfortunately, in his efforts to avoid infection the sender had thoroughly boiled these rats, so that they were not available for cultural methods. It was ascertained that rats had been dying on this boat, and also, it was said, near the wharf at Onehunga. Another rat, which was described as sick, was obtained from the boat, and on examination liver and spleen were found enlarged, and the latter showed spots of degeneration. The lung was congested and pneumonic. In spleen, lung, and blood, bacilli morphologically agreeing with Bacillus pestis were found. A guinea-pig (H) was inoculated with pulp from the rat's spleen, and this guinea-pig became ill on the third day, and on the fifth day was in a dying condition. It was killed, and on post-mortem examination the seat of inoculation showed haemorrhagic oedema, and from here a chain of enlarged glands led up to the groin and abdominal wall. The spleen was enlarged and typically mottled. The liver was congested and enlarged. There was a large pneumonic patch at the base of both lungs. Bacillus pestis was present in the enlarged glands, but could not be found in the blood. In the spleen they were scanty, but a few were found, always within the leucocytes. Bacilli were also present in the lungs. There is no doubt that the rats on this boat suffered from plague. Examination of all rats brought to the laboratory was continued throughout the year, and in June, July, September, December, and March, I visited Auckland and supervised the work. During the visit in September I detected in another rat, which had been picked up dead in a back yard near Lower Queen Street, suspicious symptoms. The spleen and liver were swollen, and the former contained bipolar-staining cocco-bacilli, which decolorised by Gram's method. Some spleen-pulp was forwarded to Wellington, while I also inoculated a guinea-pig at the Auckland laboratory. This animal died on the fifth day, and at the post-mortem all the usual plaguesjmiptoms were found, cocco-bacilli being present in glands, spleen, and blood. At the Wellington laboratory another guinea-pig was inoculated, and died after four days arid a half with similar results, and from the spleen a pure culture of Bacillus pestis was obtained on slant agar. In both these guinea-pigs the spleens were enlarged, typically mottled, and the bacilli were abundantly present.* The examination of rats has been continued systematically at Auckland throughout the year, but no further evidence of plague has been discovered. In other centres the following investigations were made in connection with suspected plague :— Gisborne. —The tissues removed at post-m,ortem on a case of a sudden death were forwarded to me for examination. No trace of Bacillus pestis was found, but an examination of the heart revealed rupture of the mitral valve. Timaru. —Some specimens forwarded by Dr. Finch from a suspicious case proved free from Bacillus pestis. * It is of some interest to note the relationship between the condition of the spleen in this series of guinea-pigs and the stage of the disease. In former outbreaks I had noticed that if the guinea-pigs were killed by artificial means after they were seriously ill, but some hours before death would naturally have occurred, the spleens, although swollen and mottled, did not contain the Bacillus pestis, though it might be abundantly present in the affected glands. In the above series this was again observed. If the animal were allowed to reach a very advanced stage of illness a few bacilli were present in the spleen, but only within the leucocytes. The guinea-pigs inoculated with the fresh spleen-pulp of the first patient died very rapidly, and in these the spleen showed no mottling, and in one dying within fifty hours of inoculation no bacilli were visible in the spleen or heart-blood. Presumably the mottling by patches of fatty degeneration is caused by the toxins present in the blood independently of the presence of the bacilli in the spleen-tissue, and the actual invasion of that organ by the bacilli only takes place at a late stage—perhaps when the blood is generally invaded. In the animals dying very rapidly the fatty degeneration of the spleen-pulp had not time to take place, and possibly in the most rapid case death took place from toxin-poisoning before the bacilli had time to thoroughly invade the blood.
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