ECOLOGY, COMMENSALISM AND PARASITISM 405 



of insects, worms, molluscs, Crustacea and lower vertebrates. 

 Severity also depends upon single or multiple infections and in the 

 ground mole, according to Schaudinn (1902), infection with Cyclo- 

 spora caryolytica is fatal in all cases. Similarly Eimeria necatrix, 

 .Johnson, is reported to be fatal to chickens in five days (Tyzzer, 

 1932). Here the sporozoites are liberated as early as one hour after 

 ingestion and penetrate the gland cells at once; this is followed by 

 rapid growth and multiplication with resulting destruction of great 

 numbers of epithelial cells and death of the host. Blood and mucus 

 containing sporocysts are passed out with the feces which becomes 

 infective material for other birds. 



( 'occidia have been reported from the greatest variety of animals, 

 both cold-blooded and hot-blooded. In mammals, Cryptosporidium 

 niuris, Tyzzer (1907), parasitic in the peptic glands is noteworthy 

 because of its minute size and its coelozoic mode of life, no intra- 

 cellular stages characteristic of the coccidia generally are known. 

 Species of the genus Eimeria are parasites in horses, cattle, pigs, 

 sheep, goats, rats, mice, rabbits, cats, skunks, squirrels. They are 

 also found in fowls, geese, ducks, pigeons, pheasants, grouse and in 

 cold-blooded forms, in frogs, newts, salamanders, tortoises, snakes 

 and fish. 



The genus Isospora (A. Schneider) differs from Eimeria chiefly 

 in the third mctagamic division, so that only 2 sporoblasts and 2 

 sporocysts are present in the oocyst. Each sporoblast gives rise to 

 2 sporozoites, the oocyst thus containing 4 instead of 8 sporozoites, 

 as in Eimeria. Like the latter genus representative species are 

 found in many different kinds of animals, both vertebrate and 

 invertebrate; here also are the only recognized pathogenic coccidia 

 of man. 



It can be easily understood that sporocysts of different kinds of 

 Sporozoa may be eaten with contaminated food. If such cysts are 

 resistant to the digestive fluids of the stomach and intestine they 

 will pass out unchanged with the feces. Such cysts found in the 

 feces may easily be interpreted as the resistant cysts of coccidian 

 parasites of the human intestine. This appears to have been the 

 case with species of the genus Eimeria in which E. clupearum, 

 Thelohan (1892), and E. sardinae, Thelohan (1890), are known 

 intestinal parasites of different fish. The cysts of these species are 

 not infrequently found, although in small numbers, in human feces. 



There seems to be little reason for doubt, however, that certain 

 species of Isospora are actually pathogenic to man. Isospora hom- 

 inis, Railliet and Lucet (190i), and I. belli, Wenyon (1923), are 

 fairly well established in this connection. Wenyon (p. 823) reports 

 an observation by Connal (1922) on a laboratory worker who 

 accidentally swallowed developed oocysts of Isospora belli; six days 

 later abdominal discomfort and diarrhea set in which lasted for 



