Probably the two most important problems now confronting those who are investigating sleeping-sickness are: (1) the method by which tsetse flies transmit sleeping sickness and other trypanosomatic infections; (2) does the trypanosome undergo a complicated (probably sexual) development in the fly?
For some time the belief has been prevalent that transmission is of the simple mechanical type, i. e., that the fly draws infected blood into its proboscis and stomach and later, when feeding on a second animal, injects some of the contaminated blood, thus transferring the disease. This conclusion has been based chiefly on the fact that the flies seemed to lose the power of transmission soon after feeding on an infected animal.
A number of experiments, however, seemed to cast doubt on the mechanical method as being the sole process, and the question has arisen as to whether there may be two methods—the first the mechanical, operating soon