320 
A STUDY OF THE DIVERSE RACES OF ENT¬ 
AMOEBA HISTOLYTICA DISTINGUISHABLE 
FROM ONE ANOTHER BY THE DIMENSIONS 
OF THEIR CYSTS. 
By CLIFFOED DOBELL 
{Imperial College of Science) 
AND MARGARET W. JEPPS 
{Bathurst Student, Newnham College, Cambridge). 
(With 7 Text-figures and Plate VI.) 
(A REPORT TO THE MEDICAL RESEARCH COMMITTEES) 
CONTENTS. 
PAGE 
Introduction ..... .... 320 
Part I. 
A. Methods used to determine the dimensions of the cysts 
of E. histolytica . . . . . . . . 321 
B. Determination of the differences in the dimensions of 
cysts when examined alive and after fixing, staining, and 
mounting: with an inquiry into the factors which deter¬ 
mine these differences ....... 323 
Pa rt 11. 
Demonstration of the exirStencc of races of E. histolytica 
whicli differ from one another in the size of the cysts 
which they produce ....... 334 
Comparison of our conclusions with those of some other workers 344 
Summary and chief conclusions ...... 349 
References ......... 350 
Description of Plate . . . . , . . . 351 
Introduction. 
In a recent paper (1917) we have drawn attention to the fact that there 
is great variation in the size of the cysts formed by the dysentery amoeba, 
1 The work here described was chiefly carried out, with the aid of grants from the 
Medical Research Committee, at the Wellcome Bureau of Scientific Research. We wish to 
record our indebtedness once more to the Bureau, for its unfailing help, and for its hospi¬ 
tality whilst the work was in progress. 
