THE NEOSPORIDIA 



421 



clear which part of the spore contains the amoebula which is liberated 

 from it, as presently to be described. 



In addition to spores having the complicated structure described for those 

 of S. tenella, there appear to be also spores of much simpler structure, as, 

 for example, in S. muris. Apparently the more complicated spore is propa- 

 gative in function, serving to infect new hosts, while the simpler form, which 

 should perhaps be regarded rather as a sporoblast, as a simple cell not differ- 

 entiated as a spore, serves for spreading the infection in the same host. The 

 occurrence of the simpler type of spore in S. muris would account for the 

 manner in which this parasite overruns its host, and is usually lethal to it, 

 while S. tenella, which appears to produce chiefly propagative spores, is a 

 harmless parasite. How far these suggestions are true must be determined 

 by future investigations. 



The discovery made by Smith, mentioned above, that mice could be infected 

 with S. muris by feeding them with the flesh of other infected mice, has been 

 confirmed and extended by other observers. According to Negre, the faeces 

 of mice which have been fed with infected muscular tissue are infective to other 

 mice* if ingested by them ; they possess this power about fifteen to sixty days 

 after the mouse was fed with muscle containing Sarcosporidia, and retain 

 their infectivity even if kept dry in an open bottle for a month, or heated to 

 65 C. for fifteen minutes. Negri was able to infect 

 gumea-pigs with S. muris by feeding them with the 

 flesh of infected mice, and found that in the guinea- 

 pig the parasite appeared with quite different char- 

 acters from those which it presents in the mouse, so 

 that it might be taken easily for a distinct species. 

 Darling also infected guinea-pigs with S. muris in 

 the same way, and points out the resemblance 

 between the experimental sarcosporidiosis of the 

 guinea-pig and a case of human sarcosporidiosis 

 observed by him ; it is suggested that the sarco- 

 sporidia occasionally observed in the human subject 

 are those of some domestic animal undergoing a 

 modified or abortive development in a host that is 

 not their usual one. Erdmann also infected mice 

 with S. tenella in a simiiar manner. It is remarkable 

 that parasites generally so harmless should be so 

 little specific to particular hosts, and the results of 

 Negri render the value of the characters used for 

 distinguishing species of Sarcosporidia as doubtful in 

 their validity as the distinctions founded on their occurrence in certain hosts. 



According to Erdmann (791), the spore germinates in the intestine of the 

 new host, and the first act in the process is the liberation from the spore of 

 its toxin, sarcocystine, which causes the adjacent epithelium of the intestine 

 to be thrown off. At the same time an amcebula is set free from the spore ; 

 and, owing to the intestine boing denuded of its lining epithelium, the amcebula 

 is able to penetrate into the lymph-spaces of the submucous coat and establish 

 itself there. Before this happens, however, the metachromatinic grains of the 

 spore disappear, and it is suggested that this disappearance is related to the 

 secretion of the sarcocystine, and that the toxin is contained in the metachro- 

 matinic grains. If, however, a polar capsule be discharged during the germina- 

 tion of the spore, as in other Cnidosporidia, it might well be that the toxin 

 is contained in the polar capsule, and is set free by its discharge, like the 

 poison in the nematocysts of the Ccelentera. However that may be, it would 

 appear as if the sarcocystine were a weapon, as it were, the function of which 

 is to facilitate the invasion of the germ, the amcebula, by destroying the lining 

 epithelium of the gut. 



The liberation of the amoebula from the spore initiates the first period 

 of the development, which is passed in the lymph-spaces of the intestine, 

 and which lasts, according to Erdmann, some twenty-eight to thirty days. 



Fia. 175. Spores of 

 Sarcocystis tenella^ 

 A, In the fresh 

 condition ; B, after 

 staining with iron- 

 hsematoxylin : N., 

 nucleus ; c, striated 

 body {polar capsule ?). 

 After Laveran and 

 Mesnil. 



