304 
Entamoeba histolytica and E. ranarum 
On examining the droppings of these tadpoles from the bottom of 
the dish, I found other free-living protozoa in them. These were 
several ciliates ( Pleuronema , Plagiopyla, etc.), and flagellates (a species 
of Bodo, etc.) which were all forms that I have at different times obtained 
from London tap-water. They were therefore probably introduced 
into the culture with the unfiltered water employed in making it. I was 
in doubt, however, whether the Umax amoeba had been introduced in 
the same way, or whether it might have come from the human faeces 
on which the tadpoles had been fed. Fortunately I was able to deter¬ 
mine this point. I happened to have kept a small quantity of this 
original faeces in a corked glass tube; and on examining it, I found that 
the same Umax amoeba had developed in it in large numbers. It there¬ 
fore appears highly probable that the faeces upon which the tadpoles were 
originally fed contained the cysts of the amoeba, which hatched in the 
water and so contaminated the culture. It may be added that the 
mortality was much higher in this culture than in any of the others; 
but whether this was in any way connected with the infection of many 
of the tadpoles with the Umax amoebae I have no means of judging. 
So far as I am aware experimental “ parasitization ” of any animal 
with free-living amoebae has not previously been achieved, though the 
occurrence of similar forms in the gut-contents of several animals has 
been recorded. I have myself described 1 a natural infection of the 
lizard with an amoeba apparently related to A. Umax. 
In the course of the experiments with cysts of E. histolytica I had an 
opportunity of observing also the behaviour of the cysts of some other 
human intestinal protozoa in their passage through the tadpole. The 
human faeces containing E. histolytica cysts, employed in the experi¬ 
ments, contained also, in some instances, the cysts of Entamoeba coli, 
Giardia (= Lamblia) intest inalis, and Chilomastix (“ Tetramitus”) 
mesnili. All of these behaved precisely alike. They passed unchanged 
through the gut of the tadpole, until they finally degenerated and died. 
The. time taken in this process was closely similar to that which I observed 
for cysts left standing in clean water. Passage through the gut of a 
tadpole appeared, therefore, to have no effect upon any of the cysts. 
These results were such as might have been foretold, for the most 
part: for an amoeba like E. coli is not found in the frog, and the frog’s 
lamblia ( Giardia agilis) is conspicuously different 2 from that of man 
1 Dobell (1914). It may be added that the so-called “Umax amoebae” described in 
the fresh faeces of human beings were probably in most cases the parasitic Entamoeba nana. 
Cf. Dobell and Jepps (1917). 2 Cf. Alexeieff (1914). 
