44 AMERICAN MUSEUM GUIDE LEAFLETS 



nature have continually come to light. The most notable recent 



„. , example is, perhaps, the African "sleeping sickness," 



Sleeping Sickness ' r I . m 



caused by a protozoan blood parasite, Trypanosoma, of 



which many species causing severe, usually fatal affections have been 



found in the circulation not only of man and the domestic animals, but 



also of reptiles and fishes. The insect which serves as the intermediary 



host is the notorious "tsetse-fly." The fatal "tsetse-fly disease" and 



the "kalaazar" or "black water fever" are two stock diseases due to this 



organism. Cattle and horses used for travel are killed by them in a 



few days. The devastation due to these diseases has been so great 



that certain districts in South Africa have had to be abandoned by the 



inhabitants. A constant supply of the parasites is obtained by the Hies 



from numerous wild animals which have in the course of time become 



immune to the disease. It has been suggested that the extinction of, 



for example, the horse on the American continent might probably have 



been due to the destructive agency of some disease-bearing insect. 1 



The discovery at Florissant, Colorado (T. D. Cockerell, 1907), of a 



fossil tsetse-fly would seem to bear out this hypothesis. 



The well-known "Texas fever" or "red water fever" 

 Texas Fever 



which has been introduced into many parts of the world 



and which has occasioned enormous losses to the cattle-breeders of the 



southwestern part of the United States is another example of a disease 



that has been conveyed by an insect, and caused by another type of 



protozoon, Piroplasma, parasitic in the blood. The insect in this case 



is the cattle tick (Margaropus annvlatus Say). The list is growing, 



and the investigations which are now being carried on, particularly by 



the German and English Governments, may prove to lie productive of 



important results. 



English investigations in India and China have jusl 

 The Bubonic , . ,. . . . „ . . , , . . , 



pia brought to light the mode or transmission ot the bacterial 



bubonic plague. It has been found that a minute flea, 

 which normally lives on gray rats, carries the disease. When the rats 

 die from the plague by thousands, the fleas find human victims anil 

 thus epidemics are produced. 



In connection with the subject of insects as carriers of disease, t In- 

 ordinary house fly should not be forgotten, since it disseminates tuber- 



1 H . ]■'. ( >sborn:The Causes of Extinction of Mammalia. The American Natural- 

 ist. Dec. 1900. 



