﻿STUDIES IN PLAGUE IMMUNITY. 183 



remaining forty-four, thirteen died and thirty-one (70 per cent) were 

 found to be immune. 



Experiments in the immunization of guinea pigs with the strain 

 "Maassen Alt." — Forty-seven guinea pigs in Series 33, 38, 40, and 

 47 (pp. 218 to 221) were inoculated either intraperitoneally or subcuta- 

 ■ neously with 1 agar culture of the strain "Maassent Alt." In the experi- 

 ments in which the inoculation was made intraperitoneally, a number 

 of the animals died of pest intoxication, namely, three in Series 33 and 

 one in Series 38. In three of these instances the cultures made at autopsy 

 from the heart's blood of the animal remained sterile ; in the fourth, no 

 cultures were taken from the heart. Two of the animals died two days 

 after the vaccination and, although in each instance cultures from the 

 heart were sterile, in both cases cultures prepared from the abdominal 

 cavity developed a rich growth of the strain "Maassen Alt." The guinea 

 pigs also occasionally died from the subcutaneous inoculation of only 1 

 agar culture of the strain "Maassen Alt ;" this was true of one in Series 40 

 and one in Series 47. In both instances the animals succumbed within 

 twenty-four hours after the vaccination, evidently of plague toxamiia. 

 Therefore, the strain "Maassen Alt" is distinctly more virulent and more 

 toxic than "Pest Avirulent." To sum up, six in all of the forty-seven 

 guinea pigs died from the effect of the vaccination. The immunity of the 

 remaining forty-one was tested from one to two months after the vaccina- 

 tion, when only five (12 per cent) died and thirty-six (88 per cent) were 

 shown to have been thoroughly immunized. One hundred and fifteen un- 

 vaccinated control guinea pigs were tested in exactly the same manner 

 and at the same time as the vaccinated ones. All of the control animals 

 died of pest infection. 



3. IMMUNIZATION WITH FILTERED CULTURES AND EXTRACTS (FREE 

 RECEPTORS) OF THE ORGANISM. 



The German Plague Commission (Gaffky, Pfeiffer, Sticker, Dieu- 

 donne) reports two experiments in the immunization of Macacus monkeys 

 with filtered bouillon cultures of the plague organism. 



A ten day's bouillon culture of the virulent bacillus was filtered through a 

 Berkefeld filter, one portion of the filtrate was heated to 60° C. and another 

 mixed with 0.5 per cent carbolic acid and put aside for twenty-four hours. One 

 of the monkeys was inoculated with 5 cubic centimeters of the first portion and 

 the other with 5 cubic centimeters of the second. On subsequently testing- the 

 immunity of these animals with 1 oese of the virulent, living pest bacillus, both 

 succumbed to the infection. 



The Austrian Plague Commission (Albrecht and Golm) found that a moderate 

 degree of immunity could be obtained in rats with filtered bouillon cultures of 

 the plague bacillus. The immunity which resulted from the use of the old 

 bouillon cultures was higher than that which came from the young ones, but 

 in neither instance did it equal that which was obtained with killed cultures of 

 the organism. 



