OF THE ALIMENTARY TRACT 217 



dom and of considerable commonness in some host 

 species, coccidia of man are not common. In fact, 

 while not rarely found in certain places, in this coun- 

 try and in most they are rare parasites. 



The complete life history of none of the species 

 of man has been observed and it is necessary, in order 

 for an understanding of its probable nature, to give 

 the cycle of a typical species, such as has been com- 

 pletely studied in some other host. 



While the life cycle of the coccidia is complex, it 

 is at the same time simple and easily understood. 

 The most confusion which comes to beginners is on 

 account of the names, difficult to a neophyte, which 

 are given to the different stages of the organ- 

 ism. These names, of course, have definite mean- 

 ings to those familiar with them but to the uninitiated 

 they are bizarre and difficult. 



While the author is not unfamiliar with coccidia in 

 certain other animals and has studied the species 

 Isospora belli, through the courtesy of others, the 

 rarity of coccidiosis of man in this country has made 

 it impossible to give any material personal observa- 

 tions, and the discussion here is largely compiled 

 from the writings of others, particularly Dobell and 

 O'Connor (1921) and Wenyon (1926). 



Description by word of the life cycle of coccidia 

 usually makes a confusing thing out of what is really 

 a simple process. It is best, therefore, to follow the 

 custom of outlining the sequence of stages by dia- 

 gram. 



