C. Dobell and M. W. Jepps 
339 
The coexistence of two strains of E. histolytica in the same patient— 
such, for example, as is seen in Case E. 130—is sometimes obvious from 
a mere inspection of a preparation containing the cysts. Nearly all 
appear to be either large or small, intermediates being either extremely 
scarce or apparently absent. In our earlier paper (1917) we noted the 
occurrence of two such double infections. (Case E. 130 is one of these.) 
But we also noted that infections occur in which cysts of large and small 
size with numerous intermediates are present; and we left it an open 
question whether such a case represents a multiple infection, or an in¬ 
fection wth a single strain producing cysts of very variable size. Cases 
E. 79 and H. 11 are two such instances; and the curves in Figs. 9 and 10 
appear to us to demonstrate the fact that each possesses in reahty a 
double infection essentially similar to that of Case E. 130. Careful 
measurements, so far as they have been made, have not yet furnished us 
with one instance of a single strain showing such great variation in the 
size of its cysts. We believe, therefore, that when cysts showing a great 
range of variation in size (e.g. 7/a-15ya) are present in a stool, a careful 
series of measurements of a sufficiently large number will probably 
reveal the fact that they belong to two—or possibly more—different 
strains. 
