354 



Marvels of Insect Life. 



disease. The doctor in charge of the sleeping-sickness patients in the hospital 

 had told him that he had found trypanosomes present in their blood, so Bruce 

 directed his inquiries to test whether these got into the blood through the attacks 

 of a flv. His researches established the fact that sleeping-sickness is caused by 

 a kindred form of low life ^ to that which produces nagana, and that the active 

 agent in its inoculation is a distinct species of tsetse-fly.^ The intervention of the 

 fly is absolutely essential to the propagation of the disease. When it sucks up the 

 blood of the animal already afflicted it also takes in many of the immature trypano- 

 somes, whose development is further advanced in the fly, and when the latter indulges 



f^~— 



Photo by] 



Fuscous Tsetse-Fly. 



[//. rsiisiiii. 



A typical sporics ol tsetse-fly, ^iliown on a much enlarged scale to make more clear its characters. It is here seen about five times 

 the actual size. 



in its next meal of blood there are sure to be some germs attached to its beak and so 

 introduced into the blood of the present victim. In the circulation of the blood 

 it finds its way to the brain, and by its action there produces the condition of coma 

 which is the outstanding symptom of the disease. Having determined the exact 

 species of tsetse-fly that is the carrying agent, Bruce found that the ravages of the 

 disease coincided with the distribution of the fly. Sleej^ing-sickness affects monkeys 

 as well as man. Dogs and rats were found to be partiallv susceptible to inoculation, 

 but efforts to infect guinea-pigs, donkeys, oxen, goats, and sheej) yielded negative 

 results. 



Thus it is shown again that though Insects may be regarded by some superior 



' 'l"i\]);inosoin.'i f^aniliiensc. - Glossina" ]ial]>alis. 



