COCCIDIOSIS IX BIRDS AND MAMMALS 301 



Cause of Sporogony. The life cycle of coccidia has heen com- 

 mon knowledge ever since Schaudinn (1900) first showed how 

 Einicria schubergi developed in the myriapod, LitJwbius, yet the 

 causal sequence between two of the phases has never been eluci- 

 dated. That the asexual cycle must start with the animal's infec- 

 tion and must continue as long as the animal remains infected 

 seems almost beyond argument, but some time during schizogony 

 the production of sexual forms leading to sporogony must start. 

 Many speculations have been hazarded as to the nature of the fac- 

 tors which bring this about, but none of them are convincing. It 

 is believed by some that after a certain number of asexual genera- 

 tions gametocytes are produced. Some think that age of the 

 host is responsible, oocysts appearing earlier in older animals. 

 Others believe that it is a question of immunity, successful anti- 

 body production of the host resulting in a chronic type of infection 

 with reduction in asexual multiplication and an increase in oocyst 

 discharge. These hypotheses should be subjected to experimental 

 test. 



Most work on coccidiosis uses as a criterion of infection the 

 presence of oocysts in the stools, and workers are prone to judge 

 the intensity of the infection by the relative numbers of oocysts 

 dejected. The truth is that the intensity of the infection, that is, 

 the damage done to the host, depends for the most part upon the 

 asexual activity of the parasites, and to a less degree upon the 

 sexual phase, of which the oocysts are the final product. It is quite 

 conceivable that the asexual cycle may proceed for a time without 

 the production of any oocysts, after which, due to the operation of 

 the proper factor or factors which result in the discharge of 

 oocysts, they may appear in the feces. An investigator following 

 such a course of events in terms of oocyst production might very 

 properly be led to believe that the second appearance of oocysts 

 was due to reinfection. If there is any quantitative relation be- 

 tween the numbers of oocysts and schizonts it should be demon- 

 strated if possible. A careful study of the course of coccidial 

 infections from a clinical point of view correlated with adequate 

 counts of oocysts discharged per day might lead to further under- 

 standing of this relation. 



Specificity. The differentiation of species of coccidia particularly 

 in those cases where there is more than one alleged species in the 

 host presents problems of prime importance. In most instances the 



