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



four distinct masses of chromatin. On the other hand, an abundant form 

 in the blood films is an indifferent type (Plate 12, figs. 18 and 19), 

 characterised usually by very short free flagellum, and it is this form which 

 develops into the female form in the fly. In this connection attention should 

 be drawn to the forms, distinctly of the female type, obtained by two of us 

 (Gray and Tulloch) in a culture (Plate 12, fig. 20, see Appendix II). 



It may be pointed out that the sexual forms of T. gamhiense from the 

 tsetse-fly are very similar to the forms of T. hrucii described by Koch* 

 from other species of Glossina, so far as can be judged from Koch's figures. 

 It is our opinion, however, that many of the forms described by Koch as 

 developmental stages of T. hrucii are really stages of one or more distinct 

 species of trypanosomes carried by the flies, comparable to, and perhaps 

 identical with, T. grayi and T. tullochii in Q. palpalis. 



At 48 hours after feeding the trypanosomes are still numerous in the 

 intestine of the fly, and a type of more indifferent character begins to make 

 its appearance (Plate 12, fig. 15). At 72 hours the trypanosomes are usually 

 beginning to become more scanty and difficult to find in the digestive tract 

 of the fly, although in some cases they are still numerous and chiefly of the 

 indifferent type. At 96 hours, in almost every case, not a single trypanosome 

 could be found even after the most careful searching. In one case a single 

 trypanosome was found, and in another case two, on the fourth day, but 

 in all other cases the trypanosomes seemed to have vanished completely 

 at this period, and could never be found at any subsequent time. It would 

 appear as if they died out with the absorption of the blood with which they 

 were ingested, and were unable to pass forward in the digestive tract into 

 the blood taken up by the fly at any subsequent feeding. In this they 

 contrast sharply with the trypanosomes described above, occurring in the 

 fly under natural conditions. 



The disappearance of T. gamhiense from the digestive tract of the tsetse-fly 

 could be interpreted in one of three ways: (1) the trypanosomes may 

 actually die out and be digested ; (2) the trypanosomes may pass from the 

 digestive tract into other organs of the fly ; (3) the trypanosomes may 

 become, by rapid division, so minute as to escape detection, like the forms of 

 Spirochceta ziemanni described by Schaudinn, or like the invisible micro- 

 organism of yellow fever. In order to test the second of these two possi- 

 bilities, the internal organs of a number of artificially infected flies were 

 carefully examined, but always with negative results, while the experimental 

 results of Bruce and ourselves seem to disprove infectivity of the fly at any 

 period after 48 hours, and, therefore, render improbable the third possibility 

 * ' Deutsch. Med. Wochenschr.,' 1905, No. 47. 



