C. Dobell 
295 
This truly remarkable resemblance has not excited the notice which 
it merits. No doubt this is largely due to the fact that, at the time 
when I described the life-history of E. ranarum, that of E. histolytica 
was imperfectly known and incorrectly described. The development 
of the cysts of E. histolytica (then supposed to belong to two other 
different species, “ E. tetragena ” and “ E. minuta ”) was wrongly inter¬ 
preted by all observers until 1911, when E. L. Walker first showed that 
it conforms to that which I described in E. ranarum. That this is so 
is now generally recognized, and from my own observations I have no 
doubts about the matter: indeed, I pointed out in 1909 that the develop¬ 
ment of the cysts of E. histolytica was probably “almost identical” with 
that of E. ranarum. But it has taken so long for the comparatively 
simple and true story of the development of E. histolytica to obtain 
recognition, in place of the fictitious and complicated accounts of the 
earlier German workers, that the observations which I made some ten 
years ago appear to have been forgotten. I recall these facts not only 
to vindicate my original account of E. ranarum, which has several 
times been called in question (but which was, nevertheless, the first 
correct description of the development of the cysts of any intestinal 
amoeba of the group to which the dysentery amoeba of man belongs), 
but also to direct attention to the close similarity of E. ranarum to 
E. histolytica —a similarity which suggested the experiments described 
in the present paper. 
When the very close resemblance of these two species is realized, 
the question naturally arises whether there may not really be something 
more than a mere similarity—in fact, an actual identity of the two 
species, E. histolytica and E. ranarum. Is it not possible that the harm¬ 
less amoeba of the frog becomes, when accidentally introduced into the 
intestine of man, the pathogenic agent of human amoebic dysentery? 
I have myself been accustomed to raise this question in my lectures for 
some years past, and in conversation and correspondence with those 
engaged in studying amoebic dysentery: and recently Alexeieff (1914) 
has made the same suggestion in print. The question can clearly be 
answered only by experiment. It is possible to attempt to infect 
human beings with E. histolytica by means of the cysts of E. ranarum: 
and conversely, to infect frogs with E. ranarum, by feeding them upon 
the cysts of E. histolytica. The former is obviously the more direct 
method of experiment, but not easily practicable. The latter is less 
direct, but is easy of trial, and is that recorded in the following pages. 
