STUDIES ON PNEUMONIC PLAGUE AND PLAGUE 

 IMMUNIZATION. 



X. IMMUNIZATION OF GUINEA PIGS BY VACCINATION WITH 

 AVIRULENT PLAGUE BACILLI MIXED WITH AGAR. 



By M. A. Barber. 

 {From the Biological Laboratory, Bureau of Science, Manila, P. I.) 



The object of this research was to test the behavior of doses 

 of an avirulent organism when mixed with agar and to com- 

 pare the immunizing effect of such doses with that of the 

 organism alone. Plague was chosen as a convenient test or- 

 ganism since it grows well in agar and has been shown by 

 Strong ^ and Kolle and Otto - to immunize about 70 to 83 per 

 cent of guinea pigs when given alone in doses of 1 to 2 agar- 

 slant-cultures. 



The mixture of the avirulent organism with agar aims at 

 the following possible advantages : 



1. A very small initial dose may be given, lessening the dan- 

 gers of anaphylactic or other intoxication ; 2, the gradual absorp- 

 tion of agar, and with it the growing colonies of bacteria and 

 their products insures dosage that is gradual and, for a time, 

 gradually increasing; 3, one inoculation may insure a dosage 

 extending over considerable time; 4, a local reaction is set up 

 by the agar which, in some cases, might favorably affect im- 

 munization. 



The technique is simple. Nutrient agar of the ordinary sort, 

 or, in some cases, made somewhat stiffer than usual, was melted, 

 cooled to about 43 °C., and a known amount of bacilli thoroughly 

 mixed with it. Quantities of the still liquid mixture, varying 



^This Journal, Sec. B (1907), 2, 155. 



^ Ztschr. f. Hyg. u. Infectionskrankh. (1903), 45, 512; 48, 399. 



245 



