COCCIDIA : CROSS-INFECTION 



exhibited an infection 5 days later. This indicates that 

 the intestinal epithelium probably allows the penetration 

 of the merozoites of natural coccidia but prevents that of 

 foreign coccidia. This method of attacking the problem 

 of host-parasite specificity can be carried further and 

 will doubtless lead to a better understanding of the sub- 

 ject. 



197 



