192 THE ANIMAL PARASITES OF MAN 



these experiments. This mode of infection a cannibalistic one 

 hardly seems likely to be the natural method for the infection of sheep 

 and ruminants generally. Smith's researches have been confirmed. 

 Negre 1 (1910) found that the faeces of mice fed on infected muscular 

 tissue were infective to other mice when ingested by them. Negri 2 

 infected guinea-pigs with S. muris by feeding them on infected mouse 

 flesh, and found that the parasite in guinea-pigs showed different 

 characters from those exhibited by it in mice. Darling 3 also succeeded 

 in infecting guinea-pigs with S. muris y and Erdmann infected mice 

 with S. tenella (from the sheep). 



According to Erdmann 4 (1910) the Sarcosporidian spore germinates 

 in the intestine of the host, which has recently ingested infected 

 material. The spore liberates its contained toxin sarcocystin 

 which acts upon the adjacent intestinal epithelium, whereby the latter 

 is shed, and an amcebula creeps out of the spore. The amcebula is 

 able to penetrate the denuded area and get directly into the lymph- 

 spaces of the submucous coat of the intestine. The first period of 

 development, lasting some twenty-eight to thirty days, is said to be 

 passed in the lymph-spaces of the intestine. Later the amcebula 

 reaches a muscle fibre. Writing in May, 1914, Erdmann 5 records the 

 appearance of small amoeboid and schizogony forms six days after 

 infection of the host. Crawley 6 (1913) controverts some of these 

 statements and considers that the Sarcosporidian spore, still sickle- 

 shaped, bores its way into the epithelial cells of the intestine and 

 comes to rest there. The spore then becomes round or elliptical, and 

 peripheral masses of chromatin appear within it, suggesting schizogony. 

 This happens about twelve hours after feeding, and in twenty-four 

 hours the spores appear to have left the intestine. More recently (May, 

 1914), Crawley 7 considers that there is sexual differentiation among the 

 Sarcosporidian spores, a few hours after their ingestion by the host. 



Interesting discussions have occurred as to the site of the toxic 

 sarcocystin within the spore. Metachromatic granules occur in the 

 middle of the Sarcosporidian spore (fig. 109), and the toxin may be 

 contained in these grains, as they disappear, according to Erdmann, 

 before the amcebula penetrates the denuded intestinal wall. However, 

 a polar capsule, containing a polar filament, may be present at one end 

 of a Sarcosporidian spore. Laveran and Mesnil described a striated 

 area at the more pointed end of the spore of S. tenella, which 

 area they consider to represent a polar capsule. Fantham 8 (1913) 



1 C. R. Soc. Biol., Ixviii, p. 997. 



2 Centralbl. f. Bakt., Orig., xlvii, p. 612 ; see also xlvii, p. 56 ; Iv, p. 373. 

 *Journ. Exptl. Med., xii, p. 19. 4 Sitz. Gesell. naturf. Frennde zu Berlin, p. 377. 

 5 Proc. Soc. Exper: BioL and Med., xi, p. 152. 6 Science, xxxvii, p. 498. 



7 Proc. A cad. Nat. Set., Philadelphia, May, 1914, p. 432. 



8 Proc. Carnbr. Philosoph. Soc., xvii, p. 221. 



