514 Sleeping Sickness 



aJive in the laboratory for 75 days and remained infective all that 

 time. Experiments directed toward finding out how long the flies 

 might remain infective in nature indicate that the flies may be able 

 to transmit the parasites for at least two years. 



It is, of course, not impossible that other flies, especially other 

 species of tsetse-flies, may act as distributing hosts of the tr3rpano- 

 somes, but there is no doubt about the chief agents being Glostina 

 palpalis and Glossina morsitans. With increased entomologic 

 and geographic information it has been found that there are certain 

 districts where these flies abound though the disease is unknown, 

 but that only shows that in those districts the flies are not infected. 

 Tsetse-flies are not, as was formerly supposed, peculiar to Africa, 

 but have been found in Arabia, where African lethargy could no 

 doubt spread should the flies become infected through imported 

 cases of the disease. The inability of the disease to spread in 

 England and America depends upon the absence of tsetse-flies from 

 those countries. 



It is possible for the disease to be transmitted from human being 

 to human being through such personal contacts as may afford oppor- 

 tunity for interchange of blood. Thus, Koch observed that in 

 certain parts of Africa where there were no tsetse-flies the wives of 

 men that had become infected in tsetse-fly countries sometimes 

 developed the disease, probably through sexual intercourse, a 

 probable explanation when one remembers that it is solely or chiefly 

 by such means that a trypanosome disease of horses — Dourine 

 or Maladie du coit, caused by Trj^anosoma equiperdum — is 

 transmitted. 



Transmission to Lower Animals.— Trypanosoma gambiense is 

 infectious for monkeys as well as for human beings. In the monkeys 

 a disease indistinguishable from the sleeping sickness is brought 

 about. It is also infective for dogs, cats, guinea-pigs, rabbits, rats, 

 mice, marmots, hedgehogs, goats, sheep, cattle, horses, and asses. 

 The lower animals are not, however, so far as is known, subject to 

 natural infection. 



Trypanosoma rhodesiense, being a more virulent parasite than its 

 close relative, probably infects a greater variety of animals. Among 

 these, in nature, antelopes seem to be commonly infected. 



Pathogenesis. — The first effect of human trypanosomiasis seems 

 to be fever of an irregular and atypical type, occurring in irregular 

 paroxysms. It was in this early febrile stage of the disease that 

 Forde and Button first found the trypanosomes in the circulating 

 blood. The number of organisms in the peripheral circulation is, 

 however, usually so small that it is tedious to look for them. The 

 search may be made in thick smears stained by any blood stain, but 

 it is better to proceed by washing the corpuscles in citrated blood 

 as in preparing to calculate the opsonic index, and to collect the 

 "leukocyte cream" for staining and examination. The trypano- 



