334 
Races of Entamoeba histolytica 
4. Assuming that the figures given above—which were obtained from 
a study of large cysts—are proportionately applicable to cysts of all 
sizes, we conclude as follows: When the processes of fixing, staining, and 
mounting are suitably conducted, so that protoplasmic contraction is 
avoided or reduced to a minimum, there is an apparent reduction of 
about 10 % in the diameter of a cyst mounted in balsam as compared 
with its true diameter in the living condition. 
Part 11. 
Demonstration of the existence of races o/E. histolytica which differ from 
one another in the size of the cysts which they produce. 
In our earlier paper (1917) we briefly noted some results obtained in 
the study of cysts from over 200 patients infected with E. histolytica. 
We pointed out that there is a very wide range of variation in the size of 
the cysts passed by difierent persons; the extreme limits which we 
observed in this respect being represented by diameters of 5p. and 20p. 
for spherical cysts, examined alive in saline solution or killed and sus¬ 
pended in iodine. The measurements which we are now about to give 
were all made upon cysts which had been previously fixed, stained, and 
mounted in balsam. In comparing them, therefore, with our former 
figures it will be necessary to introduce the correction indicated in the 
preceding section of the present paper. The cases here described -are, 
however, for the most part selected from the same series. So far as our 
technique is concerned, it will suffice to note that it has been uniform 
throughout, and is that described above. We must emphasize once more, 
however, that we have endeavoured as far as possible to eliminate the 
error due to protoplasmic shrinkage, by thorough hardening of the cysts 
before mounting them, and by omitting distorted or obviously shrunken 
cysts from our measurements. We believe, therefore, that the difference 
in the size of the cysts due to cytological manipulation approximates 
fairly closely to the ideal value to be expected from our preliminary 
investigations. Furthermore, as already noted, our conclusions are 
based upon measurements of 500 cysts in every case—250 measured by 
each of us independently. 
Measurements of the cysts from one case (E. 42) in our series have 
already been given in some detail on an earlier page (see Table I). The 
cysts of this strain of E. histolytica are of comparatively large size, the 
summit of the curve plotted from them being at 12/r for the fixed and 
stained cysts. Strains such as this are, in our experience, the commonest. 
