THE GENUS TRYPANOSOMA 263 



animals affected with the tsetse-fly disease contained the same parasite 

 as that found in nagana. In this way, after many experiments and 

 many observations, it was forced upon me that the two diseases, 

 nagana and tsetse fly, were one and the same. It is a characteristic 

 of this species of tsetse fly, Glossina morsitans, that at rare intervals, 

 probably due to long-continued drought, it overspreads its usual 

 bounds to a distance sometimes fifty or sixty miles, and so sets up an 

 epidemic among the native cattle in a previously healthy district. 

 This was the case in 1894; the disease had overspread its natural 

 bounds and given rise to a widespreading epidemic among the cattle 

 to a distance of sixty miles. 



"When it was once established that the two diseases were the 

 same, experiments were made to find out how the animals became 

 infected, whether the fly was the carrier or the mere concomitant of the 

 low-lying, unhealthy district, and, if a carrier, if it was the only carrier 

 of the disease from sick to healthy animals. Horses taken down into 



V 



the 'fly country,' and not allowed to feed or drink there, took the 

 disease. Bundles of grass and supplies of water, brought from the 

 most deadly parts of the 'fly country' to the top of Ubombo and there 

 used for fodder for healthy horses failed to convey the disease. Tsetse 

 flies caught in the low country and kept in cages on top of the 

 mountain, when fed on affected animals, were capable of giving rise 

 to the disease in healthy animals up to forty-eight hours after feeding. 

 Tsetse flies brought up from the low country and placed straightway 

 upon healthy animals were also found to give rise to the disease. The 

 flies were never found to retain the power of infection for more than 

 forty-eight hours after they had fed upon a sick animal, so that if wild 

 tsetse flies were brought up from the low country, kept without food 

 for three days, and then fed on a healthy dog, they never gave rise to 

 the disease. In this way it was proved that the tsetse fly, and it alone, 

 was the carrier of nagana. Then the question arose as to where the 

 tsetse flies obtained the trypanosomes. The flies lived among the wild 

 animals, such as buffaloes, koodoos, and other species of antelopes, and, 

 naturally, fed on them. It seemed that, in all probability, the reser- 

 voir of the disease was to be found in the wild animals. Therefore, all 

 the different species of wild animals obtainable were examined both 

 by the injection of their blood into healthy susceptible animals, and 

 also by direct microscopic examination of the blood itself. In this way 

 it was discovered that many of the wild animals harbored this try- 

 panosome in their blood. The parasites were never numerous, so that 

 it was only after a long search that they could be discovered by the 

 microscope alone. The wild animals did not seem to be affected by the 

 trypanosomes in any way; they showed no signs or symptoms of the 

 disease, and it, therefore, appeared probable that the trypanosomes 



