C. Dobell and M. W. Jepps 
347 
1. The cysts of E. histolytica possess diameters ranging from 10/a to 
15/r (living cysts). They never pass these limits. 
2. The majority of the cysts are either 12-5/x or 14-Op. in diameter. 
From 40 % to 45 % of the cysts in every infection fall under each of these 
categories—larger, smaller, and intermediate-sized cysts being excep¬ 
tional. 
3. The cyst population is thus dimorphic, consisting of “microcysts” 
and “macrocysts.” It is supposed that, on being ingested by a fresh 
host, they liberate respectively microgametes and macrogametes. 
Before considering these conclusions in detail we will briefly refer to 
the methods of investigation employed by these authors, whose results 
are so coTispicuously different from our own. It is clear, both on general 
grounds and for particular reasons considered in the earlier part of the 
present paper, that, to obtain satisfactory results in an investigation of 
the present character, the greatest attention must be paid to methods 
and technique. It is regrettable, therefore, that the authors have not 
thought it necessary to give anything but the slightest indications in 
this respect. They tell us merely that their measurements have been 
made—they do not tell us how—on stained and mounted cysts; that 
with the technique which they employed (fixation with sublimate- 
alcohol-acetic acid, staining with iron-haematoxylin and eosin) the cysts 
undergo a contraction of 2/a to 2-5/a—for which a correction is made to 
determine the size of the living cysts; and, though no adequate figures 
are given, that the dimorphism can be made evident by measuring 200 
cysts. The only curve which they give (1917 a) in illustration is, however, 
based upon the measurements of only one hundred. 
Since the authors have not yet described (so far as we are aware) their 
methods of measuring cysts—which, as we have seen, is a by no means 
simple matter—it is impossible for us to judge whether the discrepancy 
between their findings and ours depends upon differences in the tech¬ 
nique adopted. This lack of information becomes especially baffling 
when we come to consider the figures which they give for the differences 
in size between living cysts and those which have been fixed, stained, 
and mounted. The authors’ method of fixation was similar to our own; 
and their method of staining sufficiently like ours to make it probable 
that it could not account for any considerable difference in the results. 
Their statement, however, that the process of fixation, staining, and 
mounting causes a cyst to undergo a reduction of 2/a to 2-5p, in diameter 
is completely opposed to our findings. Since we have devoted much 
attention to this matter, and all our findings have been perfectly con- 
