﻿STUDIES IN PLAGUE IMMUNITY. 171 



A single animal which evidently possessed unusual resistance or acquired 

 immunity, lived for twenty-two days and finally died of chronic pest. 



Chronic forms of pest, such as have been described by Kolle and 

 Martini, 27 in which the inoculated rats lived for months, have not been 

 observed in any of the animals injected with the suspension of the strain 

 "Pest Virulent" in the doses mentioned above. It seems not unlikely 

 that less virulent strains of the organism have usually given rise to the 

 chronic infections in rats. Whenever the death of the rat occurred 

 from the infection, pest bacilli were always found at autopsy in the tissues 

 near the point of inoculation and almost always in the spleen. However, 

 in the spleen the organisms were frequently not so numerous as near the 

 point of inoculation, and in the heart's blood, while they usually were 

 present in abundance, sometimes they were found only in small numbers 

 and occasionally they even were absent. 



The Japanese variety of white rats which was used was probably the 

 albino variety of Mus rattiis. They also almost invariably succumbed to 

 pest infection in a manner similar to the wild rats and they seemed to 

 be equally or somewhat more susceptible to the same amount of the strain 

 "Pest Virulent" than the species of wild rat (Mus decumanus) . 



Whether the Manila wild rat through its progenitors has gradually 

 acquired a slightly greater insusceptibility to pest, a disease to which it 

 has been exposed from time to time, can not be stated. Albrecht and Gohn 

 found gray rats slightly more susceptible than white ones, although the 

 exjieriments upon which they based their conclusions were not numerous. 



Monkeys. — The study of pest infection in monkeys is particularly im- 

 portant, since these" animals suffer with forms of the infection analogous to 

 those seen in man and, moreover, are said sometimes to contract the disease 

 naturally. I have never observed a case of spontaneous infection in a 

 monkey in Manila, but I have never systematically sought for such an 

 infection. 



In the report of the Indian Plague Commission there is some evidence of the 

 occurrence of plague in monkeys. Most of it is not entirely conclusive, but in 

 some instances the diagnosis was confirmed by bacteriological examination. 

 Albrecht and Gohn a have also mentioned spontaneous infection in these animals 

 and Simond 2a and Clemow 30 have reported epidemics among them. 



The latter author on three occasions observed that monkeys which were sup- 

 posed to be of the species Macacus synicus, sickened spontaneously and died. 

 Plague bacilli were isolated from a number of the animals at autopsy. 



-' Deutsche med. Wchnsohr. (1902), 28, 3. 



2S Uber die Beulenpest in Bombay: Denkschr. d. .math.-naturw. Klussc d. Kais. 

 Akad., Wien (1898-1900), 66, 726. 



^ Ann. de Vinst. Pasteur (1898), 12, G64. 

 w BHt. Med. Journ. (1900), 1141. 

 55670 2 



