vi PLAGUE INDUCED IN OTHEK KODENTS 141 



plague only. Although the more or less pronounced and 

 more or less extensive character of the necrotic change in 

 the bubo, spleen, liver, and lung is no absolutely reliable 

 guide, since slight variations being noticed occasionally 

 in different guinea-pigs inoculated with the same material, 

 as a rule the more extensive and more pronounced the 

 necrotic changes are, and the longer death is delayed, the 

 less virulent may be considered the material used for 

 the inoculation. 



Observations which I have made for the Local Govern- 

 ment Board during 1905-1906, which await publication, 

 were directed to ascertain the varying susceptibility of 

 various races of rats, such as may play a part in carrying 

 plague on board ship and of disseminating it on shore. 

 These experiments, not having been published yet in full 

 by the Board, can only be indicated here in some of their 

 general results ; and in connection with it, it is in place to 

 state that Captain Liston has already drawn attention to 

 the varying susceptibility to plague of different races of 

 rats in India. 



He found that while the Indian domestic rat is very 

 susceptible to plague and dangerous as regards the trans- 

 mission of plague to man, the wild rat is less so, and 

 appears therefore to play a subordinate part in such 

 transmission. 



From a considerable number of experiments which I 

 have made, it appears that, of all rat races that 

 were tested, the tame or white rat (white, white and 

 black) is the most susceptible to plague, more so than 

 other races living in a wild state ; not only is this 

 race more highly susceptible, but it yields B. pestis, 

 originally derived from a virulent source, of a highly 



