70 THE ANIMAL PARASITES OF MAN 



bodies, enclosed in them in the transmission of the parasites to other animals. 

 Accordingly, it may be assumed that after the importation of the spores into 

 the intestine the sporozoites are set free, actively penetrate into the intes- 

 tinal cells, where they grow into coccidia, and finally become encysted. 

 The further development, i.e., the formation of spores, takes place outside 

 in these cases ; in other cases (Kloss, Eimer) it takes place within the 

 host. Although much regarding the cycle of development was still 

 hypothetical, the theories coincided with the observations, and were there- 

 fore universally regarded as confirmed. Further research confirmed this view 

 in numerous new forms. 



FIG. 28. Spores of the Coccidium cuniculi, 

 (Riv.), with two sporozoits and residual bodies ; 

 to the right a free sporozoit. (After Balbiani.) 



L. Pfeiffer's statements (13) on the part that certain coccidia or their 

 sporozoites played, or seemed to play, as causes of disease furnished 

 renewed impetus for the investigation of the coccidia. The ingestion of 

 even very numerous spores did not appear to account for the mass infection 

 so frequently observed, even after Balbiani (15) had confirmed the fact that 

 there were two, not one, sporozoites confined in every spore of the coccidia of 

 rabbits (fig. 28). The hypothesis was therefore advanced that the sporozoites 

 or young coccidia were able to divide themselves once more before again 

 sporulating. The question was finally solved quite differently. R. Pfeiffer (14) 

 first confirmed the fact that in addition to the well-known method of 



FIG. 29. So-called swarm cysts of 

 the Coccidium of the rabbit. (After R. 

 Pfeiffer.) 



sporulation in the coccidia of the rabbit that causes the infection of fresh 

 hosts ( <f exogenous sporulation "), an enormous increase may follow in the 

 already infected host in a manner that Eimer first observed in the coccidia 

 of the intestine of the mouse (" endogenous sporulation "). Whereas it 

 had hitherto been believed that some of the species of coccidia increased 

 like Coccidium oviforme and others, like Eimeria falciformis, and this difference 

 had been made the foundation of the classification. R. Pfeiffer was successful 

 in observing the occurrence of both kinds of development in the same 

 species, and expressed the opinion that endogenous sporulation, which 

 takes place within the host, was the cause of the mass-infection that is 

 mostly accompanied by serious consequences (fig. 29). L. Pfeiffer sought, 



