264 



ENTOMOLOGY 



from the fly country and fed to healthy horses failed to convey the 

 disease. 



Then the influence of the fly was tested. Tsetse flies caught in the 

 lowland, carried to the mountain and placed at once on healthy animals 

 gave rise to the disease; but the flies never retained the power of infect- 

 ing a healthy animal for more than forty-eight hours after feeding upon 

 a sick animal. Thus wild flies, kept without food for three days and 

 then fed on a healthy dog, never gave rise to the disease. The fly alone 

 transmitted the disease; and this by means of trypanosomes adhering 

 to the proboscis either inside or out. Bruce found 

 these organisms in the digestive tract also, but 

 with no change in their form. 



He discovered further that buffaloes, antelopes 

 and many other wild animals carried the parasite 

 in their blood, and was able by injecting this 

 blood to transmit the disease to healthy domesti- 

 cated animals. The parasites were never numer- 

 ous in the blood of their wild hosts, however, and 

 the latter seemed to be unaffected by their pres- 

 ence. The " big game" of Africa serves, gener- 

 ally speaking, as a reservoir for supplies of 

 trypanosomes. 



The species of parasite that Bruce studied is 

 named Trypanosoma brucei (Fig. 276). The flies 

 concerned are Glossina morsitans, G. pallidipes and 

 G. fusca, particularly the first two, the distribution 

 of which coincides with that of nagana. 



No certain remedies for the disease are yet known. ' Human serum 

 injected into infected animals causes the trypanosomes to disappear, 

 at least, temporarily; but this fact is of more scientific interest than 

 practical importance. The precaution of traveling by night is often 

 adopted. Creolin and some other substances rubbed on animals 

 serve to repel the flies, and the smoke of encampments drives them away. 

 The protection of horses by means of screens is of course effective. 



Human Trypanosomiasis. Sleeping sickness is most prevalent in 

 the Congo basin, whence it has spread rapidly in equatorial Africa, where 

 it kills about fifty thousand natives every year. The reported cases of 

 recovery are so extremely rare that the mortality is placed at one 

 hundred per cent. 



In the first stage of the disease, marked by the appearance of 



FIG. 276. Trypano- 

 soma brucei. Greatly 

 magnified. 





