20 SOME MINUTE ANIMAL PARASITES 



like extension of its body known as an undulating 

 membrane. By this membrane not only is move- 

 ment brought about, but a steadiness and grace are 

 imparted to the movements which render it more 

 smooth than that of allied organisms which are 

 not provided with a membrane. The structure and 

 life-cycle of the trypanosome responsible for sleep- 

 ing sickness may be considered as typical. 



This highly pathogenic agent (Trypanosoma gam- 

 biense) was discovered in its human victims only as 

 recently as 1901 by Forde and Button in the 

 Gambia, and by Castellani (1903) in Uganda. 

 Various sleeping sickness expeditions have been 

 sent out to Uganda by the Sleeping Sickness Com- 

 mission of the Royal Society. Under the distin- 

 guished leadership of Colonel Sir David Bruce, a 

 most important addition was made to the world's 

 knowledge of the disease. From his previous 

 brilliant researches in Zululand on "fly-disease," 

 Colonel Bruce realized the possibility of some biting 

 fly probably a tsetse being the transmitter of 

 sleeping sickness, and the result of his labours in 

 Uganda was to establish conclusively that the tsetse 

 fly, Glossina palpalis, was the carrier there of sleep- 

 ing sickness from man to man. 



Trypanosoma gambiense is a small organism, 

 measuring from 18 to 35 //., or about one-thousandth 

 of an inch long. It has a narrow, tapering, vermi- 

 form body (Fig. 4, &.), which is blunter at one end 

 than at the other. Extending down the greater 

 part of the body is a wavy extension of the body 

 wall known as the undulating membrane (Fig. 4, m.). 



