350 
Races of Entamoeba histolytica 
corrosive sublimate, two parts; absolute alcohol, one part; glacial acetic 
acid, 4-5 %.) Cysts fixed in this fluid undergo no measurable shrinkage 
or swelling in the process. 
7. The apparent loss of size observed in cysts which have been fixed, 
stained, and mounted in balsam, is due chiefly to the invisibility of the 
cyst wall in the mounting medium. 
8. It follows from what has been said above (5 and 6) that to obtain 
an approximately true value for the dimensions of the living cysts from 
measurements made upon those suitably fixed, stained, and mounted in 
balsam, these measurements should be multiplied by the factor . 
9. We find no evidence of the existence of a sexual dimorphism in the 
cysts belonging to a single race, such as has been described by Mathis 
and Mercier. 
10. Since cysts of E. histolytica may be found with all diameters from 
about 5 p to about 20p,—a range overlapping or covering the dimensions 
of the cysts of the two common harmless intestinal amoebae of man 
{E. coli and E. nana) and of other cysts and cyst-like bodies occurring in 
hiiman faeces—it is of considerable practical importance to recognize 
and distinguish the diverse races of E. histolytica which differ from one 
another in the dimensions of the cysts which they produce. 
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Dobell, C. (1909). Researches on tlie intestinal Protozoa of frogs and toads. 
Quart. Journ. Micro. Sci. liii. 201. 
-(1914). A commentary on the genetics of the ciliate Protozoa. Journ. 
Genet, iv. 131. 
- (i. 1918). Are Entamoeba histotytica and Entamoeba ranarum the same 
species? An experimental inquiry. Parasitology, x. 294. 
Dobell, C. and Jepps, M. W. (19(7). On the three common intestinal entamoebae 
of man, and their differential diagnosis. British Med. Journ. ii. 607. 
Elmassian, M. (1909). Sur une nouvelle espece amibienne chez I’liomme, Ent- 
amoeba. niiynda. n. sp. Centralbt. f. Baht. i. (Orig.) Lii. 335. 
Jennings, H. S. (1908). Heredity, variation and evolution in Protozoa. II. Proc. 
American Phil. Soc. XLVii. 393. 
Kuenen, W. a. and Swellengeebel, N. H. (1913). Die Entamoben des Men- 
schen und ihre praktische Bedeutung. Centralbt. f. Bali. i. Abt. (Orig). Lxxi. 
378. 
Mathis, C. and Mercier, L. (1916). L’amibe de la dysenteric. Bidl. Inst. Pasteur, 
XIV. 641. 
- (1916 a). Les kystes dCEntamoeba dysenieriae. C. R. Soc. Biol. Paris. 
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-- (1917). Identification des kystes des entamibes intestinales de I’liomme. 
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