238 SURRA [CH. 



but 2 ccs. of blood from each animal were injected into rabbits. 

 Three of these rabbits showed T. evansi in their blood, and after 

 some delay the three cattle thus shewn to be infected were 

 destroyed and the remainder screened. At this time there were 

 many Tabanus atratus present, together with other Tabanidae 

 and Stomoxys calcitrans. 



In subsequent series of inoculations, 13 more animals were 

 found to be infected and removed ; finally, the remainder were 

 put in fly-proof box-stalls in a fly-proof stable, and these cattle 

 all remained healthy. The authors are of the opinion that 

 Tabanus atratus was responsible for the spread of the infection 

 amongst the herd, but the results are not very conclusive, as 

 the cattle may have been infected before they arrived. 



In the Philippines, Mr M. B. Mitzmain informs me that he 

 has succeeded in obtaining the direct transmission of Surra 

 by means of Tabanus striatus. The flies were bred in captivity 

 and transmission was successful from guinea-pig to monkey, 

 and from horse to horse. In addition, this observer states that 

 T. striatus is undoubtedly the carrier of Surra in extensive 

 epidemics throughout the Philippines, and that there is a " very 

 decided correlation between the predominance of this fly and 

 outbreaks of Surra." 



On the whole, the available evidence supports the view that 

 Surra may be directly transmitted by the bites of various 

 Tabanidae, and that in nature they play a very important part 

 in the spread of the infection. It is doubtful, however, whether 

 the transmission is always mechanical, and further experiments 

 on this point are much to be desired. 



Since the above account was written, Leiper, in West Africa, 

 has discovered that two species of Chrysops serve as the inter- 

 mediate hosts of Filaria loa. At present no details are available, 

 but this discovery is especially interesting, as it is the first 

 record of any Tabanid having been shewn to be responsible 

 for the transmission of a human disease. 



