EXPERIMENTAL INOCULATION. 441 



It resists drying for four days at latest, and exposure to direct 

 sunlight for three or four hours kills it. When cultivated 

 outside the body the organism rapidly loses its virulence. 



Experimental Inoculation. Rats, mice, guinea-pigs, and 

 rabbits are susceptible to inoculation. After subcutaneous 

 injection there occurs a local inflammatory oedema, which 

 is followed by inflammatory swelling of the lymphatic glands, 

 and thereafter by a general infection. The animals die 

 usually in from one to five days, the chief changes, in addition 

 to the glandular enlargement, being congestion of internal 

 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. Monkeys also are highly susceptible to infection, 

 and it has been shown in the case of these animals that, 

 when inoculation is made on the skin surface, for example, 

 by means of a spine charged with the bacillus, the glands 

 in relation to the part may show the characteristic lesion 

 and a fatal result may follow without there being any 

 noticeable lesion at the primary seat. This fact throws 

 important light on infection by the skin in the human 

 subject. The disease may also extensively affect monkeys 

 by natural means during an epidemic. 



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. Ogata also has furnished evidence that flies and 

 mosquitoes may play a part in the spread of the disease. 



