324 
Races of Entamoeba histolytica 
alcohol, one part; glacial acetic acid, 4-5 %), and staining with Mayer’s 
haemalum; and that the mounting medium was Canada balsam dissolved 
in xylol. This procedure was adopted because it was that which, after 
a long series of trials of various methods^ made by one of us (C. D.), 
was found to give the most reliable, uniform, and rapid results in practice. 
We have long used this, therefore, as a routine method. Cysts fixed in 
this manner are not as a rule appreciably shrunken or distorted; and 
although the stain is inferior in some respects to iron-haematoxylin and 
some other methods, it permits of the study of considerable cytological 
detail, whilst demanding but a small fraction of the time, labour, and 
attention requisite for these. 
The cysts selected for the first method of investigation were obtained 
from a convalescent dysentery patient (E. 42), who had long been under 
observation, and whose cysts were of a conveniently large size. From 
a stool passed by this patient we measured 
% saline solution; 
(1) 500 living cysts in 0-75 
(2) 500 cysts in Weigert’s iodine solution; 
(3) 500 cysts fixed, stained, and mounted in Canada balsam; 
(4) 500 cysts similarly fixed and stained, but mounted in Gilson’s 
euparal. 
Our results are given in the following Table (Table I) and recorded 
graphically in Fig. 2. 
Table I. 
Dimensions of cysts in units of ocular micrometer*. 
5-5 
60 
6-5 
7-0 
7-5 
8-0 
8-5 
90 
9-5 
10-0 
10-5 
11-0 
saline 
— 
— 
— 
7 
28 
130 
108 
136 
52 
32 
3 
4 
iodine 
— 
— 
— 
16 
29 
117 
126 
134 
45 
26 
7 
— 
balsam 
1 
0 
9 
60 
90 
165 
101 
54 
12 
8 
— 
— 
euparal 
— 
1 
3 
49 
86 
166 
101 
67 
21 
5 
1 
— 
* As explained above, 1 micrometer division = l-5/r. 
^ 111 the course of this work it was found that the majority of the ordinary cytological 
fixatives give inconstant results with E. histolytica cysts, though man 3 ^ are at times excel¬ 
lent. Schaudinn’s fluid, for example (without acetic acid), frequently gives results quite 
as good as those obtained with the liquid mentioned above. Its action, however, is less 
uniform. It appears immaterial whether I % or 5 % of glacial acetic be added, but 
the addition of either more or less gave less satisfactory results. The only other fixative 
which gave equally uniform and excellent fixation was a mixture consisting of four parts 
of saturated picric acid in 1)0 % alcohol and one part of glacial acetic acid. The only objec¬ 
tion to the use of this fluid for routine work is the length of time necessary to wash out the 
2 >icric acid before staining. 
