DISEASES CAUSED BY ONE-CELLED ANIMALS 131 



diseases that they are disseminated by insects in whose 

 bodies the germs live for part of their life and undergo a 

 special part of their multiplication is one that distinguishes 

 them from the diseases caused by bacteria. However, 

 several of the bacterial diseases are undoubtedly partly 

 spread by insects, as cholera and typhoid fever by house- 

 flies, plague by fleas, etc. But the germs do not have to live 

 in the insects' bodies in order to complete their life-history. 

 However, the germs of some bacterial diseases can be, and 

 are, taken into the stomachs of the insects and passed out 

 of the body alive and virulent. The bacilli of both typhoid 

 fever and cholera have been found in 'flyspecks," which 

 are the excrement from the alimentary canal of the fly. 



