GENEKAL ORGANIZATION 



7G3 



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IN- 



other muscle fibres, so that intense infections of all the muscles may occur. 

 On the other hand, the parasite may increase steadily in size, so that after 

 seventy days it may be half a centimetre in length and contain numerous 

 cells which are apparently formed by division of those originally produced. 

 Towards the centre of the parasite some of the cells are transformed into 

 the sickle-shaped spores. With increase in size larger numbers of spores 

 are formed, and finally the characteristic structure, as described above, 

 is reached. 



Alexeiefi (1913a), in a study of the parasite of sheep, came to the 

 conclusion that the enclosing envelope consisted of three zones, the inner 

 of which is continued as the septa, 

 which enclose the uninucleated cells 

 and spores (Fig. 329). He believes 

 that the envelope, together with the 

 septa, are in reality derived from the 

 host cell, and do not belong to the 

 parasite, which is represented by the 

 round uninucleate cells which multi- 

 ply by division, and the spores into 

 which they ultimately become trans- 

 formed. According to this view, each 

 sarcocyst is not a single parasite 

 which is producing spores, but a large 

 number of uninucleate parasites en- 

 closed by an envelope and septa 

 derived from the host. Chatton and 

 Avel (1923), from a study of S.platij- 

 dactyli of the gecko, come to the con 

 elusion that the enveloping membrane 

 belongs to the parasite, and is not de- 

 veloped from the tissues of the host. 

 Negri (1908) believes that he has 

 demonstrated multiplication of the spores themselves by binary fission, 

 not only in the case of S. muris, but also S. bertrami of the horse, while 

 Teichmann (1911) claims to have made a similar observation in the case of 

 S. tenella of sheep. 



The parasites in old infections may be as much as 5 centimetres in 

 length. It is quite evident that the dimensions cannot be employed as a 

 means of distinguishing species, so that there is very little evidence that 

 the numerous species of Sarcocystis which have been described are valid. 

 Theobald Smith (1901, 1905) was the first observer to demonstrate 

 that mice could be infected by feeding them with spores. Negri (1910) 



Fig. 328. — Sareocystis muris in 

 Muscles of Mice. (After Negri, 

 1910.) 



1. Form 25 microns in length fifty days 



after feeding. 



2. Form 52 microns in length fifty days 



after feeding. 



3. Section of portion of a parasite fifty days 



after feeding. 



4. Section of portion of a parasite sixty- 



eight days after feeding. 



