220 THE AMEBIC AN NATURALIST [Vol. LI 



But the curious part of this circumstance is that the en- 

 gulfing of the parasites seems to be of slight avail in re- 

 tarding the invasion; and, in many instances without ap- 

 preciable detrimental effect upon the parasites engulfed. 

 From observations on the staining reactions and on the 

 morphological features of the ingested parasites there is 

 good evidence that Trichomonas is not disintegrated by 

 the process; and much less killed outright. It shows a 

 marked resistance to the plasm of the endothelial cells, 

 within which it frequently appears that development may 

 proceed, and from which a new generation of flagellates 

 may break out to continue the course of infection. This 

 would imply that the parasites, once engulfed, are able 

 to make use of the plasm of the endothelial cell as food. 

 And some evidence actually seems to support the view 

 that the parasites fare better in the endothelial cells than 

 they do without. In any region of invaded tissue the ma- 

 jority of the organisms are present within the engulfing 

 cells. If these views should prove valid it must be ad- 

 mitted that a curious situation is produced: the parasites, 

 to survive, must be ingested by the defensive cells, while 

 these phagocytic agents in carrying out their normal de- 

 fensive function, are favoring the growth and activity of 

 the invaders. Of course the residence of Trichomonas 

 within the endothelial cells is purely a passive cell-para- 

 sitism, although the penetration of the goblet cells is an 

 act of active cell-parasitism. But when we regard both 

 together, the matter is of considerable interest in its bear- 

 ing upon the origin of the sporozoa, cell parasites most 

 exclusively. From such elementary invasive power and 

 from such primitive toleration of unfavorable host-cell 

 influences as we see in Trichomonas, it is easy to imagine 

 how the most effective stages of sporozoan parasitism 

 may have evolved. It is a beginning of that marked 

 adaptability of form and of pliysiolouieal orga 

 which lies at the base of all pure ])araMti<ni as i 

 in the higher orders of the protozoa. 



Another noteworthy feature in tlio life of Trich 

 and one which again serves to connoct the oru'ani 



