352 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



SLEEPING SICKNESS AND OTHER DISEASES CAUSED BY 



TRYPANOSOMES 



To the group of parasitic Protozoa known as trypanosomes 

 belong some of the most important enemies of mankind. 

 These elongated, spindle-shaped, delicate little organisms, are 

 found in insects, reptiles, birds and mammals. Many of the 

 most important species are conveyed from one vertebrate host 

 to another by means of insects, the parasites often undergoing 

 some stages of their development in the invertebrate host. 



FIG. 148. Trypanosoma gambiense. Various forms from blood and cere- 

 brospinal fluid. (After Manson.) 



Trypanosoma lewisi, a parasite of rats, is perhaps the 

 best known, as it is always common wherever rats are found. 

 These parasites are transmitted from rat to rat by the common 

 rat-louse and probably also by rat-fleas. They do not seem 

 to injure the rats. Trypanosoma gambiense is the most 

 important member of this group, as it is the parasite that 

 causes the disease known as sleeping sickness, a scourge 

 that for the last few years has created more interest and 



