334 SPECIFIC MICE.O-ORGANISNS 



teria (Haffkine's method). Many modifications of the latter 

 are recommended and they constitute the practical method of 

 vaccination against plague. Hafifkine employs broth cultures 

 incubated at 25 to 30° C. for six weeks under a covering of sterile 

 oil. The cultures are killed at 65° C, and preserved with car- 

 bolic acid. The dose is o.i to 0.5 c.c. for children and 3 to 4 c.c. 

 for an adult man. It may be repeated after ten days. Good 

 results have followed the use of this prophylactic in India. KoUe 

 suspends two-day agar cultures in broth or salt solution and kills 

 at 65° C. by one to two hours exposure. Five-tenths per cent car- 

 bolic acid is then added. The dose injected is the product of one 

 agar culture. The vaccination should be taken by any physician 

 who expects to handle plague bacilli, even if only in the laboratory. 



Horses have been immunized by Yersin, injecting first killed 

 bacilli, later highly virulent bacilli, and finally the filtrates of old 

 broth cultures intravenously. The serum of these horses in a 

 dose of 20 c.c. confers a transient passive immunity, and has 

 seemed to be of value in the treatment of a few cases of plague. 

 Its preparation is so difficult and its potency so low that it has 

 not come into general use. The serum has also been injected 

 along with killed bacilli to confer immunity (combined active 

 and passive immunization) . 



The restriction and prevention of plague require measures 

 adapted to the special conditions existing. In general they include 

 precautions to exclude infected animals, wholesale destruction 

 of rats and other rodents and the artificial immunization of the 

 human population when confronted by the disease. The eradi- 

 cation of the endemic centers presents a problem of great com- 

 plexity, requiring the recognition and destruction of the infected 

 species of animals. 



Bacillus (Micrococcus)' Melitensis.^^ — Bruce in 1887 dis-' 



covered this organism in the spleen of persons suffering from Malta 



' This organism is classed as a micrococcus by most authors. It is here classed 

 as a bacillus because of its general resemblance in many of its characters to B. pestis. 

 None of the Gram-negative parasitic cocci resemble it in respect to physiological 

 characters or in the remarkable ability to change its host. ' i 



