12 PROCEEDINGS OF THE ACADEMY OF [Jan., 



situation in 9-hour stages. During the whole of this time it cannot 

 be questioned that individuals are constantly penetrating the cells. 



Therefore it seems reasonable to assume that within certain limits, 

 the intracellular spores in a given section of the upper or middle 

 parts of the intestine will be in somewhat the same developmental 

 stage. On the contrary, in the posterior part of the intestine, the 

 intracellular spores will represent a series in the development, covering 

 the greater part of the period of time elapsing between feeding and 

 the death of the mouse. Thus, in a 9-hour mouse, the parasites in 

 the cells of this extreme posterior part of the intestine might represent 

 forms which had been in the cells from only a few minutes up to 

 seven or eight hours, and in Nos. 132 and 133 it was evident that 

 this was the case. 



It further follows that in these posterior portions many more cells 

 are parasitized than elsewhere, since there is here maintained for 

 several hours a large supply of extracellular spores. 



Returning to the conditions as found in mouse 246, intracellular 

 spores in small numbers were found in int. 19, 23, and 25. These, 

 of course, represented the very earliest stages in the development 

 and in the main were not to be distinguished from those in the 

 lumen. In some cases, however, development had begun, thus 

 demonstrating the extreme rapidity with which these parasites go 

 through with their evolution. The mounted material of this mouse, 

 however, was prepared with a view of getting a general survey of 

 the conditions rather than for detailed cytologicaL study. Hence, 

 no figures of the parasites as found here have been made. 



Mouse 251. — Mouse 251 was killed 1| hours after feeding. 

 According to the observations made at the time of the infecting 

 teed, it received "a very light meal," but when the stomach and 

 intestine were prepared for study the findings suggested that whereas 

 relatively the meal may have been very light, positively such a 

 definition seemed scarcely appropriate. In the stomach, from 

 which the epithelium had largely disappeared, there were abundant 

 cysts of the parasite, many of which were more or less intact and 

 contained the greater number of the spores. In int. 1, 3, 5, and 7 

 there were abundant spores in the lumen, and in int. 9 they were 

 present both in the lumen and in the cells. 



Comparing the conditions found here with those in mouse 246, 

 it is to be noted that in the latter the spores were further back toward 

 the end of the intestine. In No. 246 the upper portions of the 

 intestine were free of spores, whereas in 251 these same portions 



