﻿III. CULTURES EMPLOYED IN THE EXPERIMENTAL WORK.. 



The cultures of Bacillus pestis employed in the experimental work 

 considered in this article consist of one virulent and three avirulent 

 strains of the organism, which will be designated in the descriptions as 

 "Pest Virulent," "Pest Avirulent," "Maassen Alt," and "Avirulent 

 Manila." 



"Pest Virulent." — The strain "Pest Virulent" was obtained from a 

 human case of plague which succumbed in October, 1905. It was isolated 

 from the spleen, at autopsy, by plate cultures and was then grown upon 

 an agar slant for one generation. From this culture it was inoculated 

 into a guinea pig. Upon the death of this animal, a portion of its 

 spleen was rubbed over a freshly shaved area on the abdomen of the 

 second guinea pig and this process of inoculation from the spleen of 

 one animal to the abdomen of a fresh one has successively been repeated 

 from animal to animal without an interruption for more than a year 

 and for over two hundred passages of the strain. (See Series of ino- 

 culations, p. 29G.) Whenever it was desirable to experiment with 

 this strain, cultures were made upon agar from the heart's blood of 

 one of this series of guinea pigs on the day of the death of the animal, 

 and twenty-four hours later the growth, if pure, was transferred to a 

 second agar tube. A second transfer of this culture (never removed 

 longer than three or four days and usually not longer than seventy-two 

 hours from the animal body) was used in my experiments in testing 

 the immunity of the animals inoculated by the different methods, except- 

 ing in a few instances in which a first transfer was employed; in these 

 eases it is so stated in the description of the experiments. Hence, the 

 method of testing was uniform, a 48-hour slant agar culture of the first 

 or second transfer invariably being employed. In the preparation of all 

 the prophylactics with which I experimented, in the manufacture of 

 which it was desired to use a virulent organism, a first or second transfer 

 of this culture was also employed. The strain "Pest Virulent" kills 

 guinea pigs, usually in from three to seven days after cutaneous ino- 

 culation by massaging the shaved abdomen of the animal with a por- 

 tion of a plague spleen from another one (see p. 296), and hence 

 it represents a very virulent strain of Bacillus pestis. It may be seen 

 from the experiments which will later be recorded in detail that, 

 during the entire time of its passage through guinea pigs, the viru- 

 lence of this strain for these animals and for rats and monkeys re- 

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