1906.] Glossina palpalis and Trypanosoma gambiense, etc. 247 



suggested above. So far then as it is possible to draw conclusions from our 

 observations, it would appear that T. gambiense does actually die out in the 

 tsetse-fly after the third day. In all cases T. gambiense was found only in 

 the mid-gut of the fly, and appeared never to pass either backwards into 

 the proctodeum or forwards into the proventriculus, another point in which 

 they contrast with the " fresh fly trypanosomes." 



(B) Observations and Experiments upon Freshly-caught Tsetse-flies Found 

 to Contain Trypanoso?nes. — When freshly-caught tsetse-flies were examined 

 by us in the laboratory, either after having been fed upon a healthy animal 

 or not, a certain percentage of them were found to contain trypanosomes 

 of one or rarely of both types referred to above as T. grayi and T. tullochii. 

 In such cases the trypanosomes were usually present in enormous numbers, 

 especially if the fly had been previously fed. These trypanosomes, when 

 compared with T. gambiense artificially introduced into a fly's intestine, are 

 distinguishable by their appearance and movements. They are far more 

 active than the sluggish gambiense, especially the male forms, which often 

 shoot across the field of the microscope with the greatest rapidity. When 

 moving in this way the body of the parasite remains nearly stiff, while the 

 forwardly directed flagellum vibrates with rapid serpentine movements. 

 In a few cases they were found in masses in the proctodeum, but in most 

 cases they occurred in the intestine, swarming and multiplying in the 

 freshly ingested blood. Occasionally they were found passing along the 

 thoracic intestine into the proventriculus. The parasites found in 

 the proventriculus did not differ appreciably either in size or appearance 

 from those found in the digestive tract. By the method suggested by Koch, 

 of compressing the bulb of the proboscis, we succeeded in forcing trypano- 

 somes out from the proboscis, but only in those flies in which the parasites 

 were found in the proventriculus. Of the two types described above, 

 T. grayi was the most commonly found, being present in l - 47 per cent, of 

 a total of 3000 flies examined, while T. tullochii was found in 0"17 per cent, 

 of flies, and both trypanosomes together in the same fly only three times. 

 When trypanosomes were found in the fly's proventriculus it was more 

 usually T. tullochii which was present, while when trypanosomes were found 

 only in the fly's intestine it was more usually T. grayi that occurred, but 

 no conclusions can be drawn from this until more flies have been examined. 



The object of our experiments on these " fresh fly trypanosornes " was to 

 determine whether one or both of the two types found were or were not 

 developmental stages of T. gambiense. As it is now beyond all doubt that 

 6r. palpalis is the agent which conveys the trypanosome of Sleeping Sickness 

 from an infected to a healthy individual, it would seem most probable at 



