CHAPTER IX. 



ANIMAL PARASITES. 



While numerous diseases are caused by vegetable parasites, such 

 as bacteria and moulds, there are others in which the etiological 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 knowledge that they are the 

 cause is lacking. Not all of the pathogens of the animal kingdom 

 will fulfil Koch's postulates but their number is increasing. 

 Within the past few years it has been found possible to cultivate 

 Trypanosomata, spirochaetae, amoebae, and hemosporidia with 

 completion 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 cocci diosis. In hydrophobia, scarlet fever, and small-pox 

 certain 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, though they will be described as such. 



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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