380 PROCEEDINGS OF THE ACADEMY OF [June. 



muscles and the percentage of positive cases are the same as when 

 the mice are fed with the stages occurring in the muscles. Negre, 

 however, was not able to detect this element in the feces and although 

 it seems as if it must be present in the intestinal tissues for a long- 

 time after inoculation, it has never been seen. Hence the evidence 

 for its existence, while entirely satisfactory, is wholly indirect. 



Negre's experiments have been repeated at the Zoological Labora- 

 tory of the Bureau of Animal Industry, and his results confirmed. 

 The impression is, however, that the infections resulting from 

 i noculation with the fecal stage are heavier than those obtained from 

 feeding infected muscle. Microscopical examination of the spores 

 obtained in this manner show them to be precisely the same as those 

 resulting from the other mode of infection. 



As we have seen, Erdmann describes multiplication stages as 

 occurring in the intestine some days after inoculation. The parasite 

 then disappears to reappear at about the forty-fifth day in the 

 muscles. Several authors have endeavored to trace the history of 

 the muscle stages, but of the several accounts the most convincing 

 is that of Negri (1910). This author worked with the white rat, 

 but the parasites of the rat and mouse seem to be identical and 

 there is no reason to suppose that the development of one would be 

 any different from that of the other. 



The smallest and hence, doubtless, the youngest stage found by 

 Negri was an elongated body, about 25 n long. It was found in a 

 rat killed 50 days after feeding. It showed a delicate bounding 

 membrane and was rather indistinctly divided into a number of oval 

 elements, each with a central differentiation. This no doubt repre- 

 sented the nucleus. Negri designates these bodies as sporoblasts. 



In somewhat larger cysts the picture is clearer, the oval sporoblasts 

 being completely individualized, and each shows a very distinct 

 nucleus. 



From this point on development appears to follow very simple 

 lines. The sporoblasts divide repeatedly by bi-partition, each 

 daughter cell coming to assume the oval form of the mother cell. 

 The parasite itself, the so-called cyst, becomes larger, but this increase 

 in size is due merely to an increase in the number of the sporoblasts, 

 which do not themselves become larger. The entire mass remains 

 separated from the host tissue by the same kind of a delicate mem- 

 brane. 



Matters proceed in this way until the cysts, according to Negri, 

 have attained a length of some 600 p-. From this time on, however, 



