XIII, B, 2 



Haughwout: Infections with Coccidium 



87 



Fig. 1. Cyst 

 of Isospora 

 cuniculi in 

 early stage 

 of develop- 

 ment. 



and conversely that the bird coccidium will not 

 infect rabbits. 



Isospora bigemina is known to be infective to 

 dogs, cats, and polecats, and is suspected of being 

 infective to man,- although Wenyon and O'Con- 

 nor (23) report negative results on feeding a kitten 

 and a mouse the developed cysts of Isospora taken 

 from a human case in Egypt. They add that Isos- 

 pora is frequently found in cats in Alexandria, but 

 that the oocyst "is quite unlike that of the human 

 parasite. The oocysts of the cat isospora resemble 

 those of the European form." 



However, the size of the oocysts is not a safe criterion on 

 which to found species any more than is the number of mero- 

 zoites formed by a schizont in the asexual phase. These varia- 

 tions are found within the species and may be almost as striking 

 as the variations found in the size of the trypanosomes. They 

 are governed largely by conditions within the host — particularly 

 in regard to the food supply. Multiple infections of epithelial 

 cells modify the parasite greatly, and these modifications ap- 

 pear in the asexual phase as reductions in the size of tropho- 

 zoites and in the number of merozoites produced and in the 

 sexual phase in the production of smaller cysts, this being rather 

 strikingly illustrated by the Coccidium found here by Dr. Elias 

 Domingo. In the strain of Isospora bigemina carried on in 

 our laboratories the cysts have been uniform in size, no very 

 striking differences having so far appeared. 



All of this probably accounts in a large degree for the lack 

 of uniformity in size of the cysts of known species as reported 

 by different observers and points out the need for added infor- 

 mation on the problems of cross-infectivity and the dangers 

 these animal species hold for human beings. 



Regarding the coccidia on which we are at 

 present working, little can be said at this time, 

 so I shall direct your attention to the illustrations 

 that accompany this article. The cysts of Doctor 

 Domingo's Coccidium tend toward the oval in 

 shape, though some are nearly spherical. The 

 oval cysts measure about 20 /x by 16 n, while 

 those that are spherical measure from 19 /*, to 

 20 (x in diameter, which brings them rather close, 

 in point of size, to the measurements recorded 



Fig. 2. Complete- ^ 



ly developed cyst by Wenyon for his human coccidium. 



of coccidium rp^g C y S £ S f Coccidium ctmiculi range from a 



cunicuh. 



