No. 604] THE CASE OF TRICHOMONAS 215 



usually accompanied by some increase in size, is marked 

 by important changes in the structures alluded to above. 

 These may be considered in some detail first with ref- 

 erence to the external features. 



Perhaps the most noteworthy change, aside from the 

 assumption of a spherical shape, involves the chromatic 

 line. This gives the appearance of lengthening until it 

 forms a hoop almost completely encircling the organism 

 (Fig. 4). It is common to see the ends of the line occupy- 

 ing positions less than 45 degrees apart as measured on 

 the circumference of the spherical flagellate. At the same 

 time the flagella have been lost and the undulatory mem- 

 brane has decreased in size, though it follows approxi- 

 mately that part of the circumference corresponding to 

 the chromatic line. Of course its functioning has been 

 proportionately reduced and although its undulatory mo- 

 tion may continue, this movement fails to cause progres- 

 sive movement of the flagellate, but brings about a slow 

 rotation of the organism in the same position. Occa- 

 sionally this movement may be assisted by a single an-, 

 terior flagellum or a remnant of one which remains after 

 the others have disappeared. In the final stage all trace 

 of the cytostome is lost, and in fresh preparations the or- 

 ganism appears as a ball of fairly homogeneous fluid, sur- 

 rounded by a granular cvtoplasm containing the nucleus 

 (Fig. 5). 



But more interesting are the changes that have been 

 occurring in the internal structures, as revealed by stained 

 preparations. The alterations in the food vacuole are 

 possibly the most significant. In the trophozoite stage 

 the vacuole was made up of one or more spaces represent- 

 ing probably not more than one eighth to one tenth of the 

 organism (Fig. 2). As the rounding-off process proceeds, 

 the vacuole increases in size until it occupies the greater 

 part of the ventral portion of the flagellate (Fig. 4). It 

 begins to crowd the c>i:oplasm against the dorsal wall, 

 and in this area lies the nucleus, which, as a result of 

 pressure, becomes somewhat flattened. At the same time 

 the "line of blocks" and the axostyle, which gives the 



