136 THE ANIMAL PARASITES OF MAN 



same phenomenon in coccidia from the epithelium of the villi and Lieberkiihn's 

 glands of the intestine of the rabbit ; but the process in this case took place in a 

 much shorter time. 



According to the discovery of Kloss (1855), the spores of the coccidia of the 

 urinary organ of the garden snail were formed in far greater numbers : the round 

 spores also harboured several (five to six) rodlets, which after the bursting of the 

 spore-envelope became free. Eimer's researches (1870) afforded information 

 regarding a Coccidium from the intestine of the mouse, which was transformed in 

 toto into a "spore," containing small sickle-shaped bodies. The fact was, moreover, 

 established that the little bodies left the delicate envelope when in the intestine, 

 made movements of flexion and extension, and were finally transformed into 

 amoeboid organisms, which apparently penetrated the epithelial cells ; at all events, 

 similar bodies of various sizes were seen in these cells. Taking the immense 

 number of these parasites into account and the lack of any other cause, Eimer 

 attributed the sudden death of his mice to the Gregarina falciformis, as the parasite 

 was then called, just in the same way as a few years previously Reincke ascribed the 

 acute and fatal intestinal catarrh of rabbits to the invasion of intestinal coccidia. 



All that had become known about coccidia up to 1879 was then compiled by 

 Leuckart, and completed by his own observations on the coccidia of the liver of the 

 rabbit. Experimental infections had already been conducted by Waldenburg (1862) 

 with intestinal coccidia of rabbits, and by Rivolta (1869-73) with the coccidia of fowls, 

 which experiments confirmed the importance of the spores, or bodies enclosed in them, 

 in the transmission of the parasites to other animals. Accordingly, it was assumed that 

 after the entry of the spores into the intestine the sporozoites were set free, actively 

 penetrated into the intestinal cells, where they grew into coccidia, and finally became 

 encysted. The further development, *>., the formation of spores, took place outside 

 the host's body in these cases ; in other cases (Kloss, Eimer) it took place within 

 the host. Although much regarding the cycle of development was still hypothetical, 

 the ideas coincided with the observations, and were therefore universally regarded as 

 established. Further research confirmed this view in numerous new forms. 



L. Pfeiffer's statements (1891) on the part that certain coccidia or their sporo- 

 zoites played, or seemed to play, as causes of disease gave a renewed impetus to 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 

 had confirmed the fact that there were two, and not one, sporozoites contained in every 

 spore of the coccidia of rabbits (fig. 72). The hypothesis was therefore advanced 

 that the sporozoites or young coccidia were able to divide once again by sporulating. 

 The question was finally solved quite differently. R. Pfeiffer (1892) first confirmed 

 the fact that in addition to the well-known method of sporulation in the coccidia of 

 the rabbit that causes the infection of fresh hosts ("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 sporula- 

 tion "). It had hitherto been believed that some of the species of coccidia increased 

 like the rabbit parasite, then known as Coccidium oviforme, and others like Eimeria 

 falciformis, and this difference had been made the foundation of a 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 (fig. 73), 

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

 accompanied by serious consequences (fig. 74). L. Pfeiffer sought, especially, to 

 demonstrate the correctness of this view as regards other species of coccidia 

 and for this purpose he utilized the experiences already published. Coccidia were 

 known to exist in a number of different hosts, and to propagate in some according 



