TO SOME DISEASES OE STOCK 
891 
trypanosomes do not live for long outside the body, and there- 
fore should the contaminated fly not require another meal, or 
should he fail to obtain one, the infection will die within a few 
hours. Usually, a sick animal is dull and lethargic or unable 
to disturb the feeding fly, which therefore obtains a full meal, 
and, when replete, does not require another bite. As a result, 
the infection of the proboscis dies out and the fly becomes 
harmless. But were it to be disturbed in the middle of its 
feed, it will immediately seek to finish the course ; and under 
the conditions of close contact occurring in a span of oxen, or 
among cattle put up in the evening into a boma, or yard, there 
is every chance of a new beast being selected at once, and the 
dirty proboscis will at entry promptly transmit infection. 
This mechanical transmission is not localised to Asia and 
America. Morocco, Algeria, Tunis, and Egypt suffer severely 
from trypanosomiasis, and yet there are no tsetse-flies. De- 
duced to smaller areas, there is evidence that outbreaks of the 
disease occur from time to time in places where no tsetse can 
be detected, and these outbreaks occur in such a progressive 
manner that it is obvious some local agent is responsible. 
Remove or destroy the affected animals, and the epidemic 
will cease — sure proof that the transmitting fly is not a true 
host or reservoir, in which case it would still be capable of 
reviving the disease. 
An outbreak which occurred two years ago on many farms 
in the Fort Hall District is an example of mechanical infection 
extending from cattle that had in all probability acquired the 
disease through the agency of tsetse-flies. 
Among Diytera, cyclical transmission of trypanosomes has 
only been proved to take place in the tsetse-flies or Glossinae. 
Such has been searched for by numerous workers with Tabanus 
and Stomoxys, but without result ; and although it should not 
be argued that vital development cannot take place in other 
biting flies it certainly appears that the Glossina is the true 
and natural host of the trypanosome in Africa. 
From the dawn of European colonisation native stock- 
owners have ascribed a poisonous influence upon their cattle 
to the tsetse : the earliest explorers confirmed that belief ; and 
in 1894, Bruce, by a series of brilliant experiments, proved that 
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