410 RESEARCH IN PROTOZOOLOGY 



because of the fact that it gives particularly definitive results 

 in the staining of segmenting forms and it stains with a readiness 

 which is to be desired in such work. The degree of reproductive 

 activity of the parasites for any given time was determined by 

 the direct method of counting the number of asexual forms of 

 the parasite in a succession of microscopic fields and noting par- 

 ticularly the ratio of segmenting forms to this total number of the 

 parasite population. Only those forms in which the process of 

 schizogony had proceeded to the point that the cytoplasm of the 

 parent individual had actually begun to divide to form merozoites 

 were included as segmenting individuals. Obviously the validity 

 of our observations is dependent upon the number of parasites 

 that were included in our counts, or the size of the sample upon 

 which the observations were made, and the size of sample used for 

 observation was necessarily greater when reproducing individuals 

 were scarce than when they were plentiful. The general rule 

 which we have followed in these studies was that of making our 

 observations upon samples of sufficient size to reduce the probable 

 error to fifteen per cent of the total observed values. Often it was 

 ten per cent, or less, but when little or no reproduction was taking 

 place it was usually unnecessary, for our purposes, to maintain 

 such a high degree of accuracy. Even under these conditions, how- 

 ever, the size of the sample was always such as to insure a 

 relatively low probability of error. 



