24 THE SOCIETY FOR THE PBESEBVATION OF 



sleeping sickness; that is to say that if, after feeding upon a man 

 whose blood contains the parasites, the fly, after an interval of 

 some 48 hours or less, bites a healthy individual, some of the 

 parasites previously taken up by the insect may escape from its 

 proboscis in an unchanged condition and so convey the disease. 

 In view of the ' rapid spread of sleeping sickness of recent years,' 

 and the fact that ' large percentages of populations, whose voca- 

 tion does not keep them constantly on the water, . . . become 

 infected ... in places where tsetse-flies are far from plentiful,' 

 the Liverpool writers consider that : ' It seems certain that such a 

 mechanical transmission cannot be the only way in which Try- 

 panosoma gamhiense is transmitted from man to man. ' The 

 conclusion arrived at by the authors in question is ' either that 

 something is wrong in the way in which Glossina palpalis has been 

 used in these experiments, or that Trypayiosoma garnhiense can 

 be conveyed by some other means than by it. ' ^ The parasite of 

 sleeping sickness has not yet been found to undergo any develop- 

 mental cycle in G. palpalis analogous to the reproduction of 

 malaria parasites in the bodies of certain mosquitoes. On this 

 account it has recently been suggested by Professor Minchin that 

 it may after all not be necessary for an infected tsetse-fly actually 

 to hite a man or domestic animal in order to convey one or other 

 form of trypanosome infection; but that the parasites in the fly's 

 intestine may, after undergoing developmental changes which are 

 at present undiscovered, pass out with the insect's dejections, and 

 so contaminate the food or drink of a subsequent vertebrate host.^ 

 In India and other parts of the East, as also in Mauritius, horses, 

 cattle, and other animals suffer from surra, which is caused by a 

 parasite closely akin to those that produce tsetse-fly disease of 

 animals, or nag ana, and sleeping sickness. The flies that have 

 been found to disseminate this malady in the Philippine Islands 

 and Mauritius belong to the genus Stomoxys, which is nearly 

 allied to Glossina. In the former locality, however, it was shown 

 experimentally, some four years ago, that sore-mouthed horses are 

 liable to contract the disease when fed on fodder contaminated 

 with surra blood and discharges from infected animals.^ 



Concluding Remarks. 

 It is well known to all who have had practical experience of 

 Glossina palpalis that, in many localities, human blood forms no 

 inconsiderable part of the diet of this species of tsetse. For the 



^ Annals of Tropical Medicine and Parasitoloqy , vol. i. No. 2 (June 15, 

 1907), p. 213. 



- E. A. Minchin, * Reports of the Sleeping Sickness Commission of the 

 Royal Society,' No. VIII., February 1907, pp. 141-142. 



^ See W. E. Musgrave, ' Preliminary Report on Trypanosomiasis 

 (Surra) in Horses in the Philippine Islands ' {Boston Medical and Surgical 

 Journal, June 25, 1903). 



