192 NON-BACTERIAL DISEASES 



The writer points out that as the disease was not epidemic 

 at the time of the experiment the possibihty of the mule having 

 become infected in any other way is " too remote to be considered," 

 and further that the strain of trypanosome used had a longer 

 incubation period, namely ten days, than most strains. Also 

 the mules had been under observation several days before the 

 experiment in a screened stable ; and their blood had been 

 examined daily. 



It is evident that this subject is an important one and requires 

 very careful investigation. 



Vazvs {Frainbcesia tropica). 



Yaws, which is a contageous and inoculable disease of the 

 tropics, characterized by ulcers of the skin, is caused by an 

 extremely delicate spirochaete, Sp. pertcnuis. 



Bancroft (1769) writing of Guiana, S. America, nearly 150 

 years ago, made the following remarks, " A small quantity of 

 yellowish pus is common seen adhering to the surface (of the 

 pustules) which is commonly covered with flies through the 

 indolence of the negroes."..." It is usually believed that this 

 disorder is communicated by the flies which have been feasting 

 on the diseased object to those persons who have sores or scratches 

 which are uncovered : and from many observations I think this 

 is not improbable, as none ever receive this disorder whose skins 

 are whole ; for which reason the whites are rarely infected ; but 

 the backs of negroes, being often raw by whipping, and suffered 

 to remain naked, they scarce ever escape." Wilson (1868) a 

 hundred years later says the belief prevails in the West Indies 

 that the disease is conveyed from one individual to another by 

 flies. 



More recently Hirsch (1896), Cadet (1897), Castellani (1907), 

 Robertson (1908) and Nicholls (191 2) have all expressed the 

 opinion that, though the disease is usually communicated by 

 direct contact, flies not infrequently distribute it, Hirsch (1896) 

 quotes two very doubtful instances of the disease being carried 

 by flies, but Castellani and Robertson quote investigations by 

 modern methods. 



