191(5.] NATURAL SCIENCES OF PHILADELPHIA. 3 



available, these representing, respectively, the 2 to 2\ hour, the 

 3 to 3| hour, and the 3 and (5 hour stages, the last being a mouse 

 given two infecting U'^U between which was an interval of 3 hours, 

 and killed 3 hours after the second meal. It was therefore con- 

 sidered desirable to obtain more material for these earlier stage-, 

 and the results to be set forth herein are based upon the examination 

 of a number of mice killed at periods of from one hour onward. 



Material and Methods. 



A list of the mice used, with appropriate explanatory matter, is 

 placed at the end of the present section. During the entire course 

 of the studies on sarcosporidiosis, every mouse obtained in whatsoever 

 manner was given a number. In many cases these were trapped 

 gray mice, or else white mice which had never been inoculated. 

 Hence those used for the microscopical study of the evolution of the 

 parasites in the cells represent but a portion of the entire series. 

 It has been considered better, how T ever, to retain the numbers origin- 

 ally given, since no confusion can possibly arise from such a procedure. 



In the list appended the time in hours elapsing between the infect- 

 ing meal and the death of the mouse has been placed immediately 

 after the number of the mouse, since this is the most important 

 datum. After this the fixing fluid is noted, and finally a statement 

 with reference to the quantity of infectious material which the 

 mouse ate is appended. The omission of these data in a number 

 of cases indicates a failure to keep the record complete. 



The list as given includes"38 mice, and the conclusions as set forth 

 herein are thus based on this number of experimental animals. It 

 is desired to lay emphasis on this point on account of the possibility 

 of confusion with other intestinal Protozoa, such as Coccidia. 



Erdmann (1914) endeavored to obtain mice in which the possi- 

 bility of extraneous infection was excluded. The procedure was to 

 raise mice from birth under as sterile conditions as possible. This, 

 of course, is the ideal method, but, as Erdmann states, it is tedious 

 and difficult. The other method is to use a large series of mice, 

 which will presumably yield results that cannot be questioned. 

 Thus, if, after feeding, parasites are found in the cells which are 

 evidently Sarcocystis spores and if, as time passes, these intracellular 

 elements undergo serial changes it would seem to be hypercritical 

 to question their identity as stages in the evolution of Sarcocystis 

 muris. For it would be necessary to assume that each experimental 

 mouse harbored Coccidia in addition to the Sarcosporidia and that 



