27G EXPERIMENTS UNDER NATURAL CONDITIONS. 



Here follows a statement (with one chart) of the results of 

 eight experiments, as to which the author i-emarks : " These 

 experiments point to the fact that the blood of animals suffering 

 from Fly Disease can retain its infective power for four clays but 

 not for seven " (p. 11). 



" (/.) Does the Tsetse-fly under natural conditions convey the 

 disease from animal to animal? 



" Having seen that the Tsetse-fly cannot of itself give rise to 

 disease ; that, on the other hand, it can readily act as a carrier, 

 and that it is able to retain its infective power for at least 

 twenty-four hours, let us now consider whether in a st/ite of 

 nature it really does convey the disease" (p. 12). 



Details and chai^ts are given of five experiments in which 

 perfectly healthy horses were taken down into the Fly Country 

 for a few hours, and were there allowed to be bitten freely by 

 Tsetse-flies, but were not permitted to eat or drink until their 

 return to the top of the hill. All the horses contracted the 

 disease, and the author writes : — " These five experiments show 

 abundantly that horses cannot, he taken loitli impumti/ for a few 

 hours into the Fly Country, even although they are not alloived to 

 eat or drink there, and they afl()rd a strong pi'esumptive proof 

 that the disease is carried to them by the Tsetse-fly. 



" This last series of experiments, hf)wever, proves less than at 

 first sight it might be supposed. It only proves that susceptible 

 animals cannot be taken into the Fly Countiy, even although 

 they are not allowed to eat or drink there. It does not absolutely 

 prove that the disease is carried to them by the Tsetse-fly. 

 There may be other ways of taking the disease, for example, by 

 inhalation. . . . This is a hard thing to understand, and in 

 order to make it possible the parasite of the Fly Disease must be 

 able to exist in some other form than that in which it is found 

 in the blood. The supposition would be that it forms a resting- 

 .stage or spore form in which it can exist as a dry, impalpable 

 dust. For my j^ai't I have much difliculty in believing that 

 animals are infected as a rule with Fly Disease by inhaling the 

 inateries morhi, and until I find animals still susceptible to the 

 disease which are protected in some way or other both from 

 feeding and the fly, I shall continue to be sceptical. 



" On account then of the lack of aljsolute proof furnished by 

 the last experiments, I set myself on the 22nd November to try 

 to infect susceptible animals with the disease by having them 

 bitten by flies brought up daily from the low country and 

 straightway placed on the animals. 



" [g.) Is the Tsetse-fly capable of giving rise to the disease if 

 taken out of the Fly Country into a healtliy locality? 



" The juethod of carrying out tliis experiment was to go down 



