486 PLAGUE 



cultures are chiefly contained in the bodies of the bacteria. 

 Injection of dead cultures in animals produces distinctly toxic 

 effects; post mortem haemorrhage in the mucous membrane 

 of the stomach, areas of necrosis in the liver and at the site 

 of inoculation, may be present. The toxic substances are 

 comparatively resistant to heat, being unaffected by an exposure 

 to 65 C. for an hour. By the injection of dead cultures in 

 suitable doses, a certain degree of immunity against the living 

 virulent bacilli is obtained, and, as first shown by Yersin, 

 Calmette, and Borrel, the serum of such immunised animals 

 confers a degree of protection on small animals such as mice. 

 On these facts the principles of preventive inoculation and 

 serum treatment, presently to be described, depend. It may 

 also be mentioned that the filtrate of a plague culture possesses 

 a very slight toxic action, and the Indian Plague Commission 

 found that such a filtrate has practically no effect in the 

 direction of conferring immunity. 



1. Preventive Inoculation Ilaffkine's Method. To prepare 

 the preventive fluid, cultures are made in flasks of bouillon with 

 drops of oil on the surface (in India Haffkine employed a 

 medium prepared by digesting goat's flesh with hydrochloric 

 acid at 140 C. and afterwards neutralising with caustic soda). 

 In such cultures stalactite growths (vide supra) form, and the 

 flasks are shaken every few days so as to break up the stalactites 

 and induce fresh crops. The flasks are kept at a temperature 

 of about 25 C., and growth is allowed to proceed for about 

 six weeks. At the end of this time sterilisation is effected by 

 exposing the contents of the flasks to 65 C. for an hour ; 

 thereafter carbolic acid is added in the proportion of '5 per cent. 

 The contents are well shaken to diffuse thoroughly the sediment 

 in the fluid, and are then distributed in small sterilised bottles 

 for use. The preventive fluid thus contains both the dead 

 bodies of the bacilli and any toxins which may be in solution. 

 It is administered by subcutaneous injection, the dose, which 

 varies according to the " strength," being on an average about 

 7 '5 c.c. Usually only one injection is made, sometimes two, 

 though the latter procedure does not appear to have any 

 advantage. The method has been systematically tested by 

 inoculating a certain proportion of the inhabitants of districts 

 exposed to infection, leaving others uninoculated, and then 

 observing the proportion of cases of disease and the mortality 

 amongst the two classes. The results of inoculation, as attested 

 by the first Indian Commission, have been distinctly satisfactory. 

 For although absolute protection is not afforded by inoculation, 



