﻿STUDIES IN PLAGUE IMMUNITY. 181 



bacilli had not as a rule invaded the circulation and other organs to 

 the same extent as they had in the control animals. 



Ten monkeys in Series 18 (p. 202) were vaccinated, each with two 

 agar cultures of the -strain "Pest A virulent." Seventeen days later, upon 

 testing the immunity of the animals, five died from the infection and five 

 survived. Animal number 1379 evidently died of plague toxaemia and 

 not of septicaemia. 



In Series 51 (p. 203), fifteen monkeys were vaccinated subcutaneously 

 with one or two 48-hour cultures of the strain "Pest A virulent." The 

 immunity of the animals was tested one month after the vaccination by 

 the subcutaneous inoculation of two-thirds of an oese of the strain "Pest 

 Virulent." Eight of the animals remained alive and seven died. 



In all, forty-four monkeys were vaccinated with the strain "Pest Aviru- 

 lent" and reinoculated with the strain "Pest Virulent;" 52 per cent of 

 these animals proved to be immune. 



Experiments with the strain "Pest Avirulent" in guinea pigs. — Seventy- 

 one guinea pigs in Series 32, 37, 39, 41, and 46 p. 204 were inoculated, 

 either intraperitoneally or subcutaneously, with from 1 to 2 agar cultures 

 of the strain "Pest Avirulent." Such large doses as two 48-hour agar 

 cultures, when injected intraperitoneally into the smaller guinea pigs 

 (150 to 175 grams in weight), frequently gave rise to the death of 

 the animals from toxaemia with, however, no evidence that a general 

 invasion by the organisms had taken place. In only one instance (guinea 

 pig number 1985, p. 205) two colonies of "Pest Avirulent" developed in 

 cultures made from the heart at autops} r . Even one agar culture injected 

 intraperitoneally caused the death of one small animal from pest intox- 

 ication, the animal dying in less than twenty-four hours after the 

 vaccination. However, when the cultures were injected subcutaneously, 

 even in small guinea pigs, death never occurred from the effect of the 

 vaccination; this was demonstrated by the inoculation of fifty-one animals. 

 (See Series 39, 41, and 46, pp. 208 to 212.) Five of the entire number 

 of seventy-one guinea pigs vaccinated with this strain died from the intra- 

 peritoneal vaccination with 2 agar cultures, one from the intraperitoneal 

 vaccination with 1 agar culture and one from an unknown cause. The 

 remaining sixty- four were tested one and two months after the vaccination, 

 whereupon forty-six (72 per cent) proved to be immune and twenty-five 

 (38 per cent) died. The test of the immunity of the animals was 

 severe and the skin was well scarified in each instance, two parallel 

 incisions being made through the dermis with a scalpel and the suspension 

 of the virulent organism rubbed into the incisions. Every one of 

 115 control animals, which were inoculated in exactly the same manner 

 and at the same time as the vaccinated animals, died of pest infection. 

 Guinea pig number 2087 was pregnant at the time of its vaccination 

 and gave birth to two healthy young, seven days after its reinoculation. 



