4 i4 PLAGUE. 



organs, sometimes with haemorrhages, and enlargement 

 of the spleen ; the bacilli are present in the lymphatic 

 glands and also, though in smaller numbers, throughout the 

 blood. Rats and mice can also be infected by feeding 

 either with pure cultures or with pieces of organs from cases 

 of the disease, and animals infected by inoculation may 

 transmit the disease to healthy animals kept along with 

 them. Kitasato considers that the disease in animals is 

 a close reproduction of the natural disease in the human 

 subject. 



There can be no doubt that this bacillus is the immediate 

 cause of the disease, and the bacteriological observations 

 throw much light on its method of spread. The affection 

 of the lower animals by the same bacilli has been 

 abundantly proved, and large numbers of dead animals 

 in the infected localities were found to contain the organism. 

 The disease was produced also by inoculation with dust 

 from infected houses, and Yersin found the organism in 

 large numbers in the bodies of dead flies in the infected 

 locality. The highly insanitary conditions under which 

 the affected individuals live give ample opportunity for the 

 direct or indirect transmission of the disease from patient 

 to patient. Kitasato considers that the bacillus may enter 

 the body by the skin surface through cracks or wounds, by 

 the respiratory passages, or by the alimentary canal. The 

 bacillus was found in the sputum in eleven out of twelve 

 cases of plague examined by Wilm, and in the faeces in 

 several where there were symptoms of enteritis. In 

 connection with an intestinal infection, it may also be 

 mentioned that in some cases where there were no external 

 buboes, a great tumefaction of the mesenteric glands has 

 been found post mortem. 



Immunity. Yersin, Calmette, and Borrel succeeded in 

 producing a certain amount of immunity in rabbits against 

 the organism by injection of cultures killed by heat at 

 58 C. They further found that the serum of such animals 

 had certain protective powers when tested in mice. 

 Later, they immunised a horse by intravenous injection 



