80 GUIDE TO THE STUDY 



birds, and other animals. Several species are reported for man 

 but infections are rare. 



PRACTICAL WORK 



Oocysts. — Coccidial infections are conveyed from animal 

 to animal by oocysts which pass out with the dung. We shall 

 begin our study with these bodies as they appear when first 

 discharged. Note their oval form, the size, the sharply con- 

 toured envelope, and the minute pore, or micropyle, at one end. 

 The protoplasmic content may fill the cyst in the early stages or 

 may be later clumped into a spherical mass. 



Development outside the Host. — The oocysts are incapable 

 of further development until they have been discharged from the 

 body of their host. In the presence of oxygen and under favor- 

 able conditions of temperature and moisture the protoplasm 

 divides into four sporoblasts. These secrete cyst walls and 

 become spores, each of which produces two sporozoites. The 

 infective oocyst thus contains four spores and eight sporozoites. 

 Make drawings illustrating the various stages. 



Development within the Host. — When ripe oocysts are ingested 

 by a rabbit, the sporozoites are liberated by the action of the 

 gastric and pancreatic juices and bore into the intestinal or 

 gall-duct epithelium. Here they undergo asexual multiplication, 

 or schizogony, and the early stages of their sexual reproduction, 

 or sporogony. 



In prepared slides of infected intestine study the following: 



Schizogony. — When the sporozoites enter the epithelial cell, 

 they become rounded schizonts and begin to increase in size. 

 In unstained preparations they are readily distinguished from 

 the host cell by their greater refractivity. As the schizont 

 develops, the nucleus divides repeatedly and finally the schizont 

 breaks up into a number of nucleated merozoites. These 

 merozoites are actively motile and enter new epithelial cells, 

 become schizonts, and continue the cycle. The infection may 

 be so extreme that large areas of tissue of the host are destroyed. 



Sporogony. — The infection of new hosts is made possible by 

 the sexual cycle, or sporogony. Certain merozoites instead of 

 developing into asexual schizonts develop as male or female gam- 

 etocytes. Unlike those of the Gregarinida, there is a marked 

 difference in the gametes and hence the cells producing the male 



