THE SPOROZOA 307 



been described, is of all species apparently the most deadly to. its host, 

 multiplying in it and overrunning the entire muscular system with 

 fatal rapidity. 



It is certain that the parasites possess the power of multiplying to 

 a dangerous extent in the tissues of their host, and it is still more 

 certain that they are able to infect fresh hosts. From all that is known 

 in other Sporozoa, it is reasonable to identify the naked gymnospores as 

 the agents in the endogenous dissemination of the parasite, comparable 

 functionally to the merozoites of Coccidiumj and to regard the chlamydo- 

 spores as destined for the infection of fresh hosts. Experimental proof of 

 these hypotheses is as yet lacking, however. The only direct evidence 

 bearing upon the dissemination of these parasites is that brought forward 

 by Smith [121], who found that mice may contract the infection of Sarco- 

 cystis muris if fed with the flesh of a mouse infested with the parasite. It is 

 extremely improbable, however, that this is the natural mode of infection. 

 It would be difficult, as Smith points out, to account for the Sarcosporidia 

 of cattle in this way. A parallel case of infection due to cannibalism has 

 been described by Schaudinn for Goccidium (see p. 221). The chief point 

 of importance established by the experiments of Smith is the fact that 

 infection takes place by way of the digestive tract, as in the vast majority 

 of Sporozoa. In this way the close proximity of the cysts, as a rule, to 

 the oesophagus and stomach receives a simple explanation. 



In Smith's experiments the gymnospores seem to have been the agents 

 of infection, since he observed no other kind of germ, but it is probable 

 that, in the natural method of cross-infection, it is the chlamydospores 

 that are concerned. This conclusion receives further support from the 

 facts stated above with regard to the death and disintegration of stale 

 spores and their continual replacement by others freshly formed ; a state 

 of things to which a parallel exists in the Myxobolidae and other tissue- 

 infecting Myxosporidia (p. 289), and also in coelomic Gregarines. It 

 may be reasonably inferred that in Sarcosporidia also the chlamydo- 

 spores are not able to develop further in the host in which they are 

 produced, but are in readiness for the moment when they can be trans- 

 ferred to another animal, failing which event, they become stale and 

 perish. We have no clue, however, to the manner in which the cross- 

 infection by the chlamydospores is effected, and nothing but surmises can 

 be put forward. 



The most remarkable feature of the chlamydospores is their extremely 

 fragile nature. Unlike the very tough and hardy spores of other Sporozoa, 

 those of Sarcosporidia betray a delicacy of constitution which must render 

 them very unfitted to brave the elements outside the body of the host. 

 For this reason many authorities l have expressed the belief that some 

 intermediate host is required, as in the case of the malarial parasite, to 

 convey the infection from one host to another. While this is an extremely 

 probable hypothesis, no facts in support of it have been as yet discovered. 

 But from the position of the parasite deep in the muscles of the host, it 

 can hardly be a blood -sucking insect, as in the case of malaria, which 



1 Wasielewski [7], p. 126 ; Lareran and Mesnil [119], p. 248. 



