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Insects aud Disease 



" (16) Chemical disinfectants do not in the ordinary 

 course of application kill plague microbes in infected 

 fleas and bugs. 



" (17) The rat flea Typhlopsylla musculi does not bite 

 human beings. 



" (18) Human fleas do bite rats. 



"(19) Fleas found on dogs and cats bite both hu- 

 man beings and rats. 



" (20) Human fleas and fleas found on cats and dogs 

 can live on rats as casual parasites, and therefore can 

 under certain conditions play a part in the transmis- 

 sion of plague from rats to human beings, and vice 

 versa." 



RESULTS OF VARIOUS INVESTIGATIONS 



Various other plague commissions from other 

 countries as well as many individuals have in- 

 vestigated the same subject, and the results all 

 point conclusively to the fact that the rats and the 

 fleas are at least the most important factors in the 

 spread of the disease. The evidence from many 

 sources and from many experiments may be briefly 

 summed up as follows: The disease is caused by 

 the presence in the system of minute bacteria, 

 Bacillus pestis. It is probable that plague is pri- 

 marily a disease of rats and only secondarily and 

 accidentally, as it were, a disease of man. 



Rats are subject to the plague and are often 



