C. Dobell 
303 
given in the usual way. On the third day I examined a tadpole, and 
was somewhat surprised to find that although it contained a great 
many cysts they were all dead and much disintegrated, many consisting 
of merely a cyst wall containing a few granules. On examining the 
remains of the human faeces left in the water in the culture dish, I found 
that in this also the cysts were in the same condition. I then put the 
culture at the ordinary laboratory temperature once more. Two 
tadpoles died shortly afterwards, and only a few dead cysts were found 
in them. The remaining five tadpoles were killed and examined on the 
14th day after feeding. In three of these I could find no cysts; but in 
the other two I found, after much searching, a very few bodies which 
I believed to be the remains of cysts. They were so far disintegrated 
that their identification was rather doubtful. 
At the higher temperature, therefore, as at the lower, the attempt to 
infect tadpoles with E. histolytica failed completely. The cysts did not 
develop in any way; they merely degenerated in the tadpoles and in 
the water with greater rapidity than before, so that after three days 
at the higher temperature they had reached a stage in degeneration 
comparable with that seen after three weeks at the lower. It seems 
probable, therefore, that E. histolytica cysts will survive much longer 
in cold than in warm water. 
A further point in connexion with one of the cultures ( A 2 ) is worth 
recording. This culture was made with unfiltered tap-water—not with 
filtered water like the others. It was a very large culture, containing 
several hundreds of tadpoles. On examining a tadpole from it on the 
16th day after they had been fed on human faeces—at a time when most 
of the E. histolytica cysts were dead—I found some small but active 
amoebae creeping about in the gut-contents. On closer examination 
these proved to be typical free-living amoebae of the Amoeba Umax 
type, with characteristic nuclei, contractile vacuoles, etc. Many other 
tadpoles in this culture were subsequently found to be infected also. 
Examination of the faeces of the tadpoles on the bottom of the dish 
showed that the amoebae were here present in vast numbers. It seemed 
clear, therefore, that the Umax amoebae had, in some way, gained access 
to the culture; and the tadpoles had evidently swallowed them with the 
faeces on which they were living. It is somewhat remarkable, however, 
that the amoebae had established themselves in the intestines of the 
living tadpoles. I had no difficulty in satisfying myself that this was 
really the case, by taking suitable precautions to avoid contamination 
of the gut-contents in removing it for examination. 
