250 Prof. Minchin, Lieut. Gray, and late Lieut. Tulloch. [July 10, 



was fed at once, and again repeatedly on successive days. After 12 days or 

 a fortnight of such daily feeding, the flies of each batch were dissected and 

 examined for the trypanosomes which they might contain. In practically 

 every case one or more flies of each batch were found to contain trypano- 

 somes, so that every experimental animal was definitely known to have been 

 fed upon repeatedly by at least one fly containing trypanosomes. Had these 

 trypanosomes therefore been identical with T. gambiense, it might have been 

 expected that at least some of these susceptible animals (such as monkeys, 

 guinea-pigs, and rats) would have become infected, but this did not occur in 

 a single instance. We thought that T. grayi might possibly be a bird-trypano- 

 some, but the negative results of feeding flies containing it on fowls did 

 not bear out this supposition. 



In addition to these feeding experiments, we inoculated other experi- 

 mental animals of the same kinds with the contents of the various parts 

 of the digestive tracts of flies containing these trypanosomes, some from the 

 proventriculus, some from the intestine and some from the proctodeum, but 

 again in every case the results were negative. 



We are, therefore, now convinced from the results of these numerous 

 experiments, of which a list is given on p. 253, that the trypanosomes 

 found in the freshly caught tsetse-flies, and referred to by us as T. grayi and 

 T. tullochii, have nothing to do with Sleeping Sickness and are not developmental 

 stages of T. gambiense. 



It is a matter of regret to us that we have not been able to establish 

 on what vertebrate host, if any, these trypanosomes are parasitic. It seemed 

 at least probable that T. grayi, some forms of which greatly resemble 

 T. johnstoni, Dutton and Todd* from Estrelda estrelda, was taken up by the 

 fly from some of the numerous water birds that haunt the lake-shore. On 

 the other hand, T. tullochii, which is very similar in its morphological 

 characters to T. gambiense, might similarly be derived from a mammalian 

 host. We may draw attention in this connection to the remarkable manner 

 in which this tsetse-fly haunts the lake-shore. There is nothing in the 

 breeding habits of the fly which should oblige it to frequent the vicinity of 

 water, as in the case of the mosquito. Our experience of flies kept in the 

 laboratory convinced us that a certain amount of moisture is necessary for 

 them, since they died much faster in their cages if not kept over water. 

 It may be supposed, however, that one attraction that the lake-shore exerts 

 upon this voracious blood-sucker is that of food-supply. Along the 

 shores of the lake and on all the small islands are vast numbers of 

 cormorants and other fish-eating birds perched with their wings extended, 



* Liverpool School of Tropical Medicine, Mem. XI, PI. 2, fig. 1. 



