442 ZOOLOGY AND MEDICINE. 



of winged insects gathered in habitations, or of larvae and nymphse 

 procured by a fine net from puddles of water, becoming not only a 

 necessary aid but even a counselor and authorized guide of the 

 hygienist and the physician. The matter becomes even still more 

 complicated, for it is useful to examine experimentally, in different 

 species of mosquitoes, the subsequent development of parasitic organ- 

 isms found in the blood of man or of animals. This leads to the most 

 delicate histological researches and the most difficult experimentation 

 well exemplified by the recent discoveries in filariosis and yellow 

 fever. 



About five hundred species of mosquitoes are known. This will 

 give an idea of the unexpected amplitude of the studies that are now 

 being pursued and of the preponderant part that entomology has 

 obtained in them. I should give a very incomplete idea of its 

 importance if I confined myself to what has just been said. Other 

 diptera also attract the attention of parasitologists, because they 

 transmit certain very fatal diseases. Everyone has heard of nagana, 

 the ejDidemic having a mysterious cause that affects European do- 

 mestic animals that are taken into certain regions of tropical Africa. 

 Livingstone recognized that it was occasioned by the sting of the 

 tse-tse fly {Glossina iriordtan.s)^ but it was a long time before the 

 actual details of the infection were understood. The problem is now 

 solved. The tse-tse inoculates cattle with a protozoan which it has 

 drawn from the blood of a sick animal ; the parasite inoculated in this 

 manner multiplies very rapidly in the l)lood of its new host and the 

 latter soon presents characteristic symptoms of nagana. 



The animalcule in question is a simple flagellate, known under the 

 name of Trypanosoma hrucei. It swims in the plasma, reproduces 

 itself there by longitudinal division, and the blood thus becomes 

 charged with more numerous parasites day by day. It is duly estab- 

 jished that these are the efficient cause of the disease which is almost 

 always fatal. The Trypanosomata are then redoubtable parasites 

 and their history ought to especially interest the physician if it is 

 proved that the human species may also be attacked by similar 

 organisms. 



Now the malady of sleeping sickness, which flourishes in tropical 

 Africa with dreadful intensity, so that it devastates very extensive 

 territories, as it has done during recent years on the Kongo and in 

 Uganda, is nothing less than a trypanosomosis. The specific pai-asite 

 is here the TrypanosoTna gamhiense, that is transmitted by the 

 Glossina palpalis and, apparently, by other species of trypanosomata 

 whose agents of transmission are not Glossinm but Muscidw of other 

 types or various Tahanidce. Still further it is known that there 

 exists in Algeria a human trypanosomosis which, in view of the 

 absence of Glosshuv in that region, must also be placed in the latter 



