428 MICROBIOLOGY 



Recently Tyzzer l has reported a study of coccidiosis in 

 the rabbit in which he points out that they attack only the 

 epithelial cells and that at the termination of the process of 

 growth of the parasite, the cell is reduced to simply a sac con- 

 taining the parasite having on one side a deeply stained 

 crescent.* 



Several species of coccidia have been described. They 

 have been found in many animals and occasionally as the 

 cause of serious parasitism. The following species are more 

 commonly encountered. The condition resulting from the 

 invasion of coccidia is known as coccidiosis. Rabbits affected 

 with coccidiosis exhibit livers with nodules which frequently 

 have been mistaken for tuberculosis. The hepatic parenchyma 

 is studded or literally filled with whitish yellow cysts varying 

 in size from a millet seed to that of a pea or even larger. They 

 are globular or elongated in shape. They may be present in 

 very large numbers in which case the liver is enlarged and 

 covered with nodular protuberances. The cysts contain a 

 thick, yellowish, grumous or caseous matter chiefly composed 

 of the encysted coccidia, epithelial cells in the state of fatty 

 degeneration, free nuclei and fat globules. The membrane 

 lining these nodules is simply the altered wall of a hepatic 

 canal which under the influence of irritation has developed a 

 somewhat thick capsule of connective tissue. 



1 Tyzzer. Jour, of Med. Research, Vol. II (1902) p. 235. 



* Calkins has pointed out very clearly the well recognized bio- 

 logical principle that degeneration is an inevitable outcome of con- 

 tinued parasitism (Lankaster degeneration). While the degenera- 

 tion of the usual vegetative organs is the result of parasitism, the 

 restricted mode of life of the parasite may require certain conditions 

 which may lead to structural adaptations on its part. This tends to 

 decrease the chances of the parasite. In order to overcome this, the 

 biological fact has been observed that the number of offspring of an 

 animal is in inverse proportion to the chances of reaching maturity 

 and that the number is great enough to maintain the species. With 

 the great group of protozoa it is expected that some of them would 

 have acquired a parasitic mode of life. 



