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299 
tadpoles, in order to ensure that it contained a large number of mature 
(quadrinucleate) and healthy cysts. 
The tadpoles were allowed to continue feeding upon the infected 
faeces as long as they would do so. At the end of two or three weeks, 
little or none of the original faeces was usually discoverable, and the 
bottoms of the culture dishes were covered with fine debris and numerous 
coils of tadpole faeces which seemed no longer attractive to them— 
probably because the material had lost its nutritive value with repeated 
passage through their bodies. From this stage onwards I fed the tad¬ 
poles on finely minced meat, or human faeces from persons who, as I 
determined by frequent examination of their stools, were free from 
infection with E. histolytica. The water in the cultures was renewed 
from time to time, when necessary, the old and dirty water being siphoned 
off and fresh filtered tap-water substituted. 
As already noted, the tadpoles fed on human faeces remained very 
healthy and throve exceedingly. Those which were not killed for 
examination finally underwent partial—a few of them complete—meta¬ 
morphosis before the cultures were finally abandoned. I examined the 
intestinal contents of a few tadpoles every day, or every few days, after 
they had begun to feed on the infective material. I did this in the follow¬ 
ing way. A tadpole which had fed on faeces (easily determined, because 
the faeces in the intestine is clearly visible through the transparent 
belly-wall of the living tadpole) was removed from the dish, killed by 
decapitation, and its gut removed entire with needles and placed upon 
a slide. The gut was then slit open from end to end, and the contents 
mixed and spread out in a few drops of Ringer’s fluid. The preparation 
was then covered with a coverglass and examined under the microscope. 
At first I examined the entire contents of the intestine, but with increase 
in size this became impossible. I therefore examined in this way a few 
samples of the gut-contents taken from different parts of the intestine. 
When the large intestine had become differentiated I usually confined 
my examination to this part only, as it is the seat of infection with 
E. ranarum in the adult frog. From time to time I also examined the 
coils of faeces dropped on the bottoms of the culture dishes by the tad¬ 
poles; and also the remains of the infected human faeces, so long as 
there were any, to see whether living cysts were still present. All the 
findings were carefully recorded from day to day. 
All the experiments led to practically the same result. It is therefore 
unnecessary to give the individual records for each culture. The tad¬ 
poles in some cultures were examined more frequently than those in 
