PROTOZOA AND DISEASE 2OI 



lum from one end. Species of trypanosomes occur fre- 

 quently in the blood of various animals, without neces- 

 sarily giving rise to any 

 ill effects. Others are 

 extremely dangerous, one 

 producing the disease 

 called " sleeping sickness " 

 in man, another the na- Drawing by ^ eber (after 



gana disease Of domestic ^ Wellcome Research Laboratories) . 



animals in Africa. The FlG ' ' Trypanosome of camel, greatly 



magnified. 



Ciliata or ciliate Protozoa 



are usually thought of as free living, but even these in- 

 clude parasites, such for example as the Opalina, com- 

 mon in -the frog. This is an oval species, capable of 

 being extended to look like a worm. The most charac- The 

 teristic parasitic Protozoa are, however, the Sporozoa, or s P rozoa 

 "spore animals," which have neither cilia nor flagella, 

 and reproduce mainly by the formation of spores, or 

 small particles arising in great numbers at one time from 

 the parent. Here we include a division called Hemo- 

 sporidia, living in blood, members of which cause malaria, 

 tick fever, and apparently Rocky Mountain spotted 

 fever. 



4. It is not difficult to understand how the organism Alternate 

 of dysentery, which occupies the alimentary canal, can paras iti c 

 be acquired through drinking infected water. In tropi- Protozoa 

 cal countries the prudent traveler boils all his water, or 

 uses distilled water. But what about the malaria para- 

 site, found in the blood, or that of sleeping sickness, also 

 inhabiting the internal fluids ? Can these animals, in 

 the course of one or a few generations, pass into the ali- 

 mentary canal, and thence into the blood ? The sup- 

 posed course of evolution is not thus repeated, nor does 

 it appear that the origin of parasitism in these types 



