KesseJ: Amoebae of Cultuie Rats and Mice 



505 



while in E. coli, the four races distinguished have mean diameters of 

 15, 16.5, 18.7, and 21.7ju, respectively. 



In C. muris the cysts vary in diameter from 13/x (pi. 44, fig. 16) 

 to 19/i (pi. 45, fig. 23). Measurements of cysts have been made from 

 the material stained in iron-haematoxylin and three distinct races 

 have been determined, one with an average diameter of 14.5/;t, a second 

 with an average of 15.7/i, and a third with an average of 17.7/i. The 

 accompan3'ing table gives the range, average diameter, standard devia- 

 tion, coefficient of dispersion, and variability in percent of the differ- 

 ent races of C. muris. Cross-infection experiments of CoiincUmania 

 muris to non-infected rats have produced no racial change in the size 

 of the cysts. 



TABLE 5 



Cytoplasm and inclusions. — The cy topla.sm in the cysts of C. m u ris 

 in structure looks like an accumulation of fine flakes. Stained with 

 iron-haematoxylin it assumes a gray appearance and the darker inclu- 

 sions within the cyst may be distinguished easily. This flaky structure 

 of the cytoplasm can be distinguished definitely from the alveolar type 

 of cytoplasm found in E. dysenteriac and from the more coarsely 

 granular cytoplasm of E. coli. 



Three types of structures within the cytoplasm of the cyst are to 

 be distinguished, namely, the nuclei, and two types of inclusions, the 

 glycogen ma.ss and the chromatoidal bodies. 



The glycogen mass, though present in the cysts at the time of 

 fixation, is dissolved out by water during the process of staining and 

 leaves merely a large clear vacuole. This vacuole is predominantly 

 present in the mononucleate and binucleate cysts (pi. 43, fig. 7 ; pi. 44, 

 fig. 11). An occasional mononucleate cyst is found without a glycogen 

 vacuole (pi. 44, fig. 9), but it is significant to note that no binucleate 

 cysts without glycogen vacuoles have been discovered. As the glycogen 

 is probably utilized in the metabolic processes attendant upon mitosis, 

 it seems likely that a mononucleate cyst without glycogen cannot com- 

 plete development. Around the margin of the glycogen vacuole chro- 

 matoidal bodies often appear (pi. 44, fig. 15). As the chromatoidal 



