2Q2 SOME MINUTE ANIMAL PARASITES 



directly, for more work is put upon such organs owing 

 to the failure of the liver's action. Parasites such as 

 Schizotrypanum cruzi and Leucocytogregarina funambuli 

 that form cysts in the lungs of their hosts interrupt 

 the aeration of the blood, and hence produce some 

 degree of anaemia. 



In conformity with the mode of life of parasitic 

 Protozoa, it is most important to them that the life 

 of their host should be prolonged. They are depen- 

 dent on it both for food and shelter, and in some 

 cases the death of the host brings about the destruc- 

 tion of the parasites. But once a parasite is 

 established in its host, its need for shelter and food 

 is at an end, and consequently the organism ceases 

 to provide elaborate apparatus for the capture and 

 digestion of food. Even parasitic Ciliates reduce the 

 size of their cell mouths and gullets and decrease the 

 number of their cilia. But with decrease in com- 

 plexity of organization, there comes also an increase 

 in the powers of reproduction. Large numbers of 

 offspring are necessary in order to maintain the race. 

 They may be Destined merely to overrun the host 

 animal or to pass from one host to another, the 

 latter passage being far the more difficult and 

 dangerous. The ideal host for any parasite, natur- 

 ally, is one that can tolerate the presence of the 

 intruder for the longest period without ceasing to 

 afford nourishment for the latter by the impairment 

 of its own health. Once the reaction of the host 

 against the parasite has commenced, and the pro- 

 tozoon has produced resistant forms, the death of 

 the host may provide the channel of escape for the 



