PROTOZOA IN THE DIGESTIVE TRACT 13 



sometimes recognized as indistinct rings. In addition, there 

 may be seen a vacuole, and refractile, colorless rods which 

 become deeph^ stained in permanent preparation and are 

 known as chromatoid bodies. The c)'sts measure 5-20[j in 

 diameter. 



When the cysts are stained with Lugol's solution (p. 57), 

 the c\ toplasm becomes tinted in grayish l:)rown color and 

 the nuclei are easily recognized. In many cysts there may 

 be found one or more ill-defined masses which are stained 

 reddish brown (the glycogen bodies), while the rod-like 

 chromatoid bodies remain colorless. Thus Lugol's solution 

 facilitates greatly the identification of the cyst. 



2. Stained specimens. When the cysts (Fig. 1, 6-8) are 

 fixed and stained (p. 58), the cvst wall remains unstained 

 and is not noticeable as its index of refraction is nearly the 

 same as that of the mounting medium, Canada balsam. 

 The cytoplasm appears fineK^ reticulated and may show 

 vacuolation especially in young uninucleate cysts (Fig. 1, 

 6). Such vacuoles as a rule contain glycogen. There are seen 

 one to several rod-like bodies which stain intensely black. 

 These are the so-called chromatoid bodies which in this 

 species are almost always with rounded extremities. The 

 nucleus in young uni- and bi-nucleate cysts may appear 

 somewhat different in structure from that of the trophozoite 

 described above, as in many cases the nuclei are preparing 

 for, or completing, division (Fig. 1, 6). But when the nuclear 

 divisions are completed, there are seen four small nuclei, 

 about 2m in diameter, of the structure more closely re- 

 sembling that of the trophozoite (Fig. 1, ^^ ^). Some of the 

 four nuclei may divide once more on rare occasions so that 

 cysts with six to eight nuclei may be seen. These are con- 



