PROTOZOA AND DISEASE 



205 



These look somewhat like house flies, but are recognized 

 by the long, straight proboscis projecting in front of the 

 head, and by the way in which the wings are folded over 



From drawing by Jo/in T. Scott 



FIG. 44. Tsetse fly (Glossina palpalis), female; X 5 diameters. From a speci- 

 men collected in Southern Nigeria, Africa, by G. Garden, April 28, ioog. This 

 fly is widely distributed over tropical Africa. It has a formidable proboscis, and 

 sucks the blood of man and other animals. In so doing, it transmits a minute 

 protozoan, called Trypanosoma gambiense, which produces in man and monkeys 

 the disease known as " sleeping sickness." From this disease many thousands of 

 the inhabitants of Africa have perished. Another related protozoan, Trypanosoma 

 brucei, is carried by a different tsetse fly, Glossina morsitans, and produces in cattle 

 and horses the highly fatal disease called " nagana." Tsetse flies once existed in 

 Colorado, as is proved by fossils found at Florissant. They may well have trans- 

 mitted the organisms causing disease, and thus been instrumental in extermi- 

 nating some of the larger animals. Thus we find here, as throughout the realm 

 of animate nature, that all living things are actors in the great drama of exist- 

 ence, and those which seem at first to have the most insignificant parts often 

 prove able to influence an ever widening circle of events. Man and his affairs can- 

 not be understood without reference to the humblest forms of life. 



