C. Dobell 
305 
(G. intestinalis). With Chilomastix, however, the case is different, for the 
species found in frogs (Ch. caulleryi) is so like that of man (Ch. mesnili) 
that Alexeieff (1914) has even suggested that they are the same. As 
this is a possibility not to be ignored, I devoted some further attention 
to it, beyond the incidental observations made during the experiments 
with E. histolytica cysts. On July 17, 1916, I fed some of the surviving 
tadpoles in culture B 2 —w T hich I had previously failed to infect with 
E. histolytica —on human faeces containing an immense number of 
healthy cysts of Chilomastix mesnili. I examined some tadpoles on the 
21st, 22nd, 27th and 28th of July, and found, as before, that the cysts 
passed through them quite intact. By July 28th (11 days after first 
feeding) the cysts were nearly all dead, but none of them appeared to 
have undergone any development. They were still present in fairly 
large numbers in the intestines of the tadpoles and in their droppings 
on the bottom of the culture dish. 
I conclude from these observations that the cysts of Ch. mesnili will 
not develop in the tadpole; and consequently that Ch. mesnili Wenyon 
and Ch. caulleryi Alexeieff—parasitic in man and frog respectively—are 
probably, in spite of their close resemblance, quite distinct species. 
I have not myself studied the cysts of the parasite-of frogs, though the 
flagellates have been known to me since 1907; but according to the 
brief account of them by Alexeieff (1912) they appear to be almost 
identical with those with which I am very familiar in the faeces of man 1 . 
Discussion of Results. 
The experiments just recorded afford no support for the hypothesis 
that Entamoeba histolytica and E. ranarum are merely two forms of the 
same species inhabiting two different hosts. It is now certain, since 
the experimental work of Walker and Sellards (1913), that man becomes 
infected with E. histolytica by swallowing the cysts of the parasite; and 
it is highly probable, though not yet experimentally proved, that the 
frog similarly acquires an infection with E. ranarum by swallowing the 
cysts of this species. But it seems legitimate to conclude, from the 
experiments here described, that the cysts of E. histolytica pass, when 
ingested, unchanged through the intestine of the frog. They do not 
undergo any development in this host, and thereby establish in it an 
entamoebic infection. It seems highly probable, therefore, that the 
cysts of E. histolytica and those of E. ranarum, in spite of their very 
close resemblance, are in some way different from one another. This 
1 Cf. Dobell and Jepps (1917). 
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