C. Dobell and M. W. Jepps 
335 
We find, however, that there are strains which produce cysts having a 
mean size either smaller or greater than this. Strains of much smaller 
size—the commonest being those with an average diameter of 7 /x to 8p,—■ 
are not uncommon; but strains with a diameter considerably greater are 
by no means common. We have already (1917) noted that, in a series of 
over 200 E. histolytica infections which we studied, over 30 % were in¬ 
fections with cysts of the smaller sizes. But we have seen so few 
infections with cysts having a mean diameter greater than 14/a that 
we are at present unable to form any accurate estimate of their real 
frequency. 
In the following table (Table IV) we give the results of four series of 
measurements of the cysts from four different carriers of E. histolytica. 
The measurements, as before, are all given in units of the micrometer 
scale—not in microns. Case E. 42 has already been recorded (see Table 
I, line 3), but is repeated here for comparison with the others. 
Table IV. 
Measurements of cysts belonging to four different strains of E. histolytica. 
Dimensions of cysts (in balsam) 
Case No. 
3-d~ 
3-5 
4-0 
4-5 
50 
5-5 
6-0 
6-5 
7-0 
7-5 
H. 8. ... 
8 
33 
194 
140 
102 
19 
3 
1 
— 
— 
H. 7 
1 
6 
44 
93 
205 
105 
37 
8 
1 
— 
E. 42 ... 
— 
— 
— 
— 
— 
1 
0 
9 
60 
90 
B. 1 
— 
— 
— 
— 
— 
— 
1 
1 
11 
18 
Dimensions of cysts (in 
balsam) 
Case No. 
H. 8 
H. 7 
E. 42 ... 
8-6’ 
8-5 
9-0 
9-5 
10-0 
10-5 
11-0 
11-5 
120 
12-5 
165 
101 
54 
12 
8 
_ 
_ 
_ 
_ 
_ 
B. 1' ... 
57 
92 
152 
71 
55 
23 
5 
7 
6 
1 
This table displays very clearly the differences in the dimensions of 
the cysts in these four races. The differences are, however, seen in a still 
more striking manner in the figures^ reproduced in Plate VI, and in the 
curves plotted from the measurements. To facilitate comparison we 
have plotted the four series together in a single chart (Fig. 4). In this, 
as in the others, the units of measurement have been converted into 
microns. It will be seen that the summit of the curve for each race falls 
^ X full exjJanation of these figures is given in the description of the plate. 
