PARASITISM AMONG PROTOZOA 



103 



habiting the lower intestine of white ants (termites), transform 

 the wood eaten by a termite into soluble sugars on which the 

 termite, as well as its guests, thrive. Ingenious experiments by 



Fig. 58— A WORKING PARTNER 



Trichonympha campanula, a complex 



flagellated protozoan which changes 



solid wood into soluble sugar for 



white ants 



From a photomicrograph by the author 

 Magnification, 150 



the American biologist, Dr. L. R. Cleveland (1892- ) have 



demonstrated that termites if deprived of these associates die 

 of starvation. 



Harmful Associations 



There is no doubt that many kinds of protozoa in the intes- 

 tines live by absorption of food digested by the host and to this 

 extent rob the host of nutriment, but when compared with the 

 food absorbed by a tapeworm, for instance, such loss is negli- 

 gible. A more serious situation is provided by those forms 

 which lie among the cells lining the wall of the intestine and 

 which break down the functioning cells of the host by secreting 

 their own digestive fluids. In this way Endamoeba dysenteriae 

 causes the ulcers and abscesses in the intestines and liver which 

 are characteristic of amebic dysentery. 



Once adapted to the conditions of the digestive tract, fur- 

 ther adaptations which may lead to progressive parasitism are 

 always possible. Thus the flagellates Herpetomonas and Lep- 

 tomonas are harmless parasites of the digestive tracts of lower 

 animals, but a closely related genus, Crithidia, has progressed a 

 step farther in parasitism and plants itself in great numbers on 



