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host, as in the case of the tsetse, the hypopharynx of which swarms 

 with trypanosomes, so that whenever it bites an animal it is bound to 

 inoculate it. Other biting flies, which are not true hosts, may, after 

 biting an infected animal, carry an infective trypanosome for some 

 hours in its proboscis and in biting a healthy animal may 

 mechanically infect it with the still dangerous trypanosome in its 

 saliva ; in this case the chance of infectivity is in inverse proportion 

 to the length of time that has elapsed between the two feeds. Non- 

 biting flies may also transfer trypanosmes on their feet or proboscis 

 from a sore on one beast to that on another. It is by mechanical 

 infection that the trypanosomes of surra are transferred from one 

 animal to another by Tabanus, Haetnatopota an^ Stomoxys, and in 

 Central Africa this is frequently the method of transmission. Mechani- 

 cal infection by Glossina is not strictly analogous with mechanical 

 infection by flies other than tsetse, because in the one case the 

 trypanosomes remain healthy, being in their true host, while in flies 

 of other genera the trypanosomes are in an unhealthy environment 

 and tend to die out rapidly. In the case of Stomoxys, the proboscis 

 is said to be uninfective 1| minutes after the fly has fed on surra- 

 infected blood. 



In 1914, the author inoculated a dog with T. brucei vel rJiodesiense. 

 Living with it was another dog, both being much Avorried by Stomoxys 

 and other Muscids biting their ears. After a time the second dog was 

 found to be suffering from trypanosomes similar to those found in the 

 other animal. In a Rhodesian farming district which is a fly-free 

 area almost completely surrounded by fly-infested land, the author 

 was impressed by the disproportion between the large number of 

 animals infected and the small number or absence of tsetse in the 

 neighbourhood of the outbreak. While the initial cause of the out- 

 break might well be a stray tsetse, it seemed probable that the disease 

 was spread in the herd by some other agency. In another case a 

 thousand village cattle were examined just as the rains were com- 

 mencing and less than a dozen proved to be infected. Six months 

 later, in the same village, 500 of the cattle previously examined were 

 found to be either dead or very ill from trypanosomiasis. On neither 

 occasion was a tsetse- fly seen in the vicinity, although occasional 

 individuals were seen in neighbouring areas. The author considers this 

 seasonal occurrence of the disease, which is coincident with that of other 

 biting flies, to be significant, when it is considered that out of 300 cattle 

 kept for one month in a thin fly belt, only 20 animals became infected. 

 Finally, on estates where the danger from mechanical infection is 

 realised and measures are taken to isolate all infected animals, no fresh 

 oases occurred during the following rainy season, although severe 

 outbreaks had previously been the rule. The conclusions are drawn, 

 that it is unwise to allow cattle infected with trypanosomes to run 

 with healthy animals, particularly during the rainy season, but that 

 the mere passage of infected animals in the vicinity of healthy cattle 

 is not dangerous to the latter. 



In a note appended to this paper, the chief veterinary surgeon 

 remarks that while trypanosomiasis in domestic animals may in some 

 areas be transmitted by flies other than tsetse, he believes this to be 

 very rare in Southern Rhodesia. 



(C382) a2 



