BACILLUS PESTIS 377 



or of cholera patients is mixed with similar cultures of the 

 typhoid or the cholera bacillus. (See Agglutinins). 



Protective Inoculation; Vaccination. — Active immunization 

 from plague infection by protective inoculation has been 

 variously attempted; by subcutaneous or intramuscular 

 injection of old bouillon cultures of bacillus pestis that had 

 been killed by heat; by similar injections of emulsions made 

 from agar-agar cultures of different ages suspended in 

 isotonic salt solution and likewise killed by heat; by the 

 injection of determined amounts of extractives from plague 

 bacilli; by the injection of mixtures of dead plague bacilli 

 and plague immune serum; by injection of the filtrate from 

 fluid cultures of the organism; by the injections of peri- 

 toneal exudates and organ extracts of animals infected with 

 plague; and by the injection of attenuated living cultures 

 of the organism. For the most part these efforts have been 

 experimental, that is to say, they have been made upon 

 animals susceptible to plague infection, notably guinea-pigs 

 and monkeys. In the problem of protecting human beings 

 from plague, dead cultures have been used practically to 

 the exclusion of all other methods. The method of Haffkine' 

 has enjoyed more favor than any of the others, though it 

 is difficult to determine its protective value with any degree 

 of exactness.^ This method consists in the subcutaneous 

 injection of from 0.5 c.c. to 7.0 c.c. of a six weeks' old, 

 specially prepared bouillon culture of bacillus pestis that 

 had been killed by exposure to 65° C. for one hour. Some- 

 times the smaller, sometimes the larger doses are indicated; 

 sometimes a single injection is given, sometimes several are 

 repeated at shorter or longer intervals according to circum- 



1 British Med. Jour., 1897, No. 12. 



2 Bull. del'Inatitut Pasteur, 1906, No. 4, p. 825. 



