No. 604] THE CASE OF TRICHOMONAS 



221 



the accepted type of sporozoan parasitism deals with the 

 manner of obtaining its food. It has already been pointed 

 out that when the trophozoites are developing in the in- 

 testinal contents they ingest large numbers of bacteria; 

 whether, at this time, osmosis plays any part in cell nutri- 

 tion is a question. When Trichomonas has entered the 

 deeper tissues, however, the situation is different, since 

 there are ordinarily few bacteria in these regions. Here 

 it seems that nutrition by osmosis must play an important 

 role in supporting the life of the rapidly multiplying or- 

 ganisms. It thus appears that Trichomonas is sufficiently 

 adaptive to new conditions of existence in the. tissues to 

 substitute an osmotic method of nutrition for the in- 

 gestive. This nutrition by osmosis it will be at once 

 recognized is one of the characteristic features of the 

 sporozoa, and here again is to be seen a link connecting 

 these two protozoan types. 



But there is another point of interest involved in this 

 change in the manner of nutrition when Trichomonas 

 enters upon its tissue despoiling career, and this concerns 

 the influence of the manner of nutrition upon some of the 

 morphological features of the parasites. 



In regarding the appearance of the flagellates pre- 

 ceding their invasion of the tissues, and after they have 

 gained a foothold in the submucosa, a marked difference 

 is to be observed. This has already been mentioned and 

 may be so great as to deceive one into the belief that the 

 parasites which are found in the intact crj^jts and which 

 penetrate the epithelial wall, are not identical in nature 

 with the organisms occurring in the deeper tissues. It is 

 this difference which has led some writers to believe that 

 we are dealing with two different protozoan forms. The 

 difference lies primarily in the following circumstance: 

 In the cecal content the flagellates are represented by two 

 forms, the motile trophozoite and the encysted organism. 

 In the case of the latter, one can usually ()bs(M-vo cloarly 

 the large ball of reserve-substance, and tli(^ rdalivi'ly large 

 daughter nuclei. When developinc: in tlio lissuos, on the 

 other hand, although the motile forms can be recognized 



