CHAPTER IX 

 ANIMAL PARASITES 



While numerous diseases are caused by vegetable parasites, 

 such as bacteria and moulds, there are others in which the etio- 

 logical role is played by minute microscopic organisms of the 

 animal kingdom. There are also infectious diseases that are 

 supposedly caused by animal parasites, and yet the exact knowl- 

 edge that they are the cause is lacking. Not all of the pathogens 

 of the animal kingdom will fulfil Koch's postulates but their num- 

 ber is increasing. Within the past few years it has been found 

 possible to cultivate Trypanosomata, spirochaetee, amoebae, and 

 hemosporidia with completipn of Koch's postulates in the first two. 



In general, it may be said of animal parasites, particularly those 

 belonging to the protozoa, that an intermediate host, such as a 

 suctorial insect, is necessary for the transmission of the organism 

 to man or animal. This is called alternate generation and is a 

 very characteristic feature. 



The protozoa, as parasites in man, are the cause of several well- 

 known diseases, namely: dysentery, malaria, sleeping-sickness, 

 and coccidiosis. In hydrophobia, scarlet fever, and small-pox cer- 

 tain peculiar bodies are constantly found that resemble protozoa, 

 but since it is not known whether they are animal bodies at all, 

 they cannot be classed as protozoa, and are discussed under 

 Chlamydozoa in the next chapter. 



PROTOZOA 



The protozoa of importance as disease producers are to be found 

 in the classes, orders and families given as follows: 



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