302 
Entamoeba histolytica and E. ranarum 
In the foregoing experiments I examined altogether 160 tadpoles 
at various times after they had fed upon human faeces containing cysts 
belonging to seven different strains of E. histolytica. The number is not 
enormous, but is, I think, quite sufficient to demonstrate that the cysts 
will not undergo development in the tadpole. The time and trouble 
necessary for the examination of even a single tadpole are considerable. 
Long before I had examined the last I had convinced myself that the 
experiments were a complete failure, so far as infection was concerned. 
I wished, however, to establish beyond question the fact that infection 
is impossible, and I regret that my time was too fully occupied to allow 
me to examine more tadpoles. The experiments, though not absolutely 
conclusive from a statistical point of view, have convinced me at all events 
that a tadpole, however abundantly fed with cysts of E. histolytica, will 
not, in all probability, acquire as a result an infection with E. ranarum. 
Since none of the experimental tadpoles became infected with 
Entamoebae the examination of those in the control cultures became 
almost a work of supererogation. For the sake of completeness, however, 
I examined at various times 40 tadpoles from the control cultures A v B v 
and C v They were all completely negative for free or encysted Ent¬ 
amoebae or any other protozoa, as was to be expected. It should be 
added that the controls were fed upon cooked meat or vegetables, and 
one of them (Bj) also with human faeces free from cysts of E. histolytica. 
They all remained active and healthy to the last, and displayed no 
features of special interest. 
No detailed mention has so far been made of subcultixre B 5 . This 
was a very small culture containing only eight tadpoles, which were taken 
from the control culture B 1 about a month after the eggs had hatched. 
As I had at this time satisfied myself that the tadpoles in the other 
cultures were not becoming infected with Entamoebae, it occurred to 
me that the temperature at which the experiments were made might 
possibly influence the result. All the cultures had previously been 
kept at the ordinary temperature of the laboratory, and I therefore 
determined to make some similar experiments with cultures kept at higher 
temperatures. Unfortunately it was very difficult with the means at my 
disposal to maintain a large culture at a constant high temperature; 
and in addition the tadpoles, when the temperature of the water was 
raised considerably, appeared extremely uncomfortable and refused to 
feed. With subculture B 5 , however, I succeeded in keeping them for 
three days at a temperature of 32-5° C., during which time they fed 
upon human faeces containing abundant living E. histolytica cysts 
