342 
Races of Entamoeba histolytica 
It is to be noted, however, that a patient infected with two difierent 
strains at the same time may present an apparent exception to this rule. 
As is now well known, cysts are not always present in the stool of an 
infected person—or, at all events, are not always present in discoverable 
numbers. From time to time the stools are negative. Now it is clear 
that a person infected with two different strains may sometimes be 
negative for either or both. If, therefore, at a single examination cysts 
of large size are present, it cannot be concluded that the patient is in¬ 
fected Avith this strain only. At the next or at a later examination cysts 
of small size may be found, either alone or accompanied by the larger 
cysts. A careful study of such a case by more prolonged examination 
and the measurement of a large series of cysts will alone enable one to 
arrive at the correct interpretation. One of our cases (E. 58) furnishes 
us with a case in point. This man, when first examined, was found to 
be passing numerous cysts of E. histolytica of large size—mostly from 
12/X-14/X in diameter. A second specimen, examined at a later date, 
contained cysts which at first sight appeared to be all of small size 
(8ju,-9)u,). A careful study of this stool, however, revealed the faQt that 
large-sized cysts were also present in very small numbers; and a series 
of measurements clearly showed that we were dealing with a double 
infection similar to those which we have already described. The diameters 
of the two strains were 8p,-9p, and 12p,-14p,. Cases such as this, there¬ 
fore, though apparently indicating at first sight an inconstancy in the 
size of the cysts, in reality, when carefully studied, furnish most con¬ 
clusive evidence of the constancy of the different strains of E. histolytica. 
We believe, however, that certain conditions may, to a slight extent, 
temporarily modify the size of the cysts of a given strain. Although we 
can adduce no large series of measurements in support of our behef, we 
have often observed a slight increase in the size of the cysts from a 
patient just relapsing after unsuccessful treatment with emetine. These 
cysts are usually very degenerate, and frequently all uninucleate. In 
the case of the larger strains (12p,-14/x before treatment) they may be 
15/i, or more in diameter; such large cysts constituting the great majority 
—not, as originally, the rare exceptions—among the cysts in the stool. 
These large and deg^ierate cysts often give rise to considerable diffi¬ 
culties or uncertainties in diagnosis. We have invariably found, however, 
that, after a few days, cysts of normal size and structure reappear in the 
stools; thus enabling one not only to confirm the diagnosis, but also to 
verify the fact that the administration of emetine has brought about no 
permanent change in the size of the cysts. 
