NON-BACTERIAL DISEASES 191 



Trypanosomiasis. 



It is well known that biting flies of the genus Glossina are 

 responsible for the spread of sleeping sickness, the most im- 

 portant human trypanosome disease, and possibly other biting 

 flies may transmit other forms of trypanosomiasis. It appears, 

 however, from Darling's (19 12) work that M. domestica may be 

 responsible for the spread of a trypanosome disease in mules in 

 the Panama Canal Zone. He found that mules and horses were 

 equally susceptible to the disease, caused by Tr. Jiippicuni, but 

 that " when they were stalled together, mules developed the 

 disease, but saddle horses never became infected." " The mules, 

 from the nature of their work, frequently suffered from ' scraper 

 cuts,' galls, and other injuries in which the skin became broken, 

 while such injuries were rarely noted on the saddle horses." 

 Darling thought that flies visiting the excoriated patches carried 

 the disease, and proceeded to confirm his view by experiments. 



"Three lots oi Rlusca domestica were caught and each was placed in a biting jar. 

 A guinea-pig richly infected with Trypanosoma hippictim was bled from the ear. 

 Two or three drops of blood were placed on the centre of a glass plate which was 

 inverted over the biting area of the jar containing the flies. Jar A contained about 

 eighteen flies, jar B nine, and jar C six. A number of the flies in each jar were seen 

 to feed on the guinea-pig's blood, those in jar A being hungrier than the others. 



"The glass plate with the guinea-pig blood was carefully replaced by a towel that 

 was used to wipe away any possible droplet of blood that might have touched the 

 rim of the jar, or that might have been deposited near the rim by the flies. This was 

 done to prevent any possible inoculation of the mule by guinea-pig blood that might 

 be on the margin of the jar. The towel was replaced by a clean glass plate that was 

 slipped out when the biting area of the jar was placed over the recently shaved, scratched 

 skin of the mule. In each experiment the flies were exposed to the guinea-pig blood 

 for three or four minutes, and then, after an interval of about thirty seconds, were 

 placed over the scratched skin of the mules where they remained for about five 

 minutes. As the flies were not hungry they fed with some difficulty, and, as the 

 experiment was conducted out of doors in bright sunshine, they sought the opposite 

 end of the jar, and could be made to visit the scratched skin only by covering the jar 

 and making it quite dark. On this account the conditions of the experiment were 

 probably not as favourable for infecting as they would have been under natural 

 conditions in a corral, yet after a period of ten days, the usual incubation period in 

 mules for the strain of Trypanosoma hippictim employed, the temperature of one 

 of the animals rose to 103° F., and its blood contained Trypanosoma hippiatnt. The 

 other two mules have shown no signs of infection. 



"The mule that became infected had been exposed to the flies in jar A, which 

 contained about eighteen active, vigorous specimens that had been caught about two 

 hours before the experiment." 



