945 
To judge from the facts which have been brought out in this work, 
we conclude that the manner of invasion is similar to that belonging to 
other infections. The primary action seems to be due to a_ toxic 
secretion which is a product of the amcebic symbiosis, acting upon the 
exposed cells of the mucous membrane. It is likely that, in addition to 
considering the chemistry of symbiotic products, we can not ignore the 
receptive condition of the cells themselves, influenced, as they may have 
been, by their evironment. It is probable that the mechanism of the 
intestinal infection does not materially differ from that taking place in 
the liver and other organs, excepting that it is more complex because of 
the mixed and changing environment to which the amcebe are exposed. 
In discussing the production of liver abscess it has already been pointed 
out by Musgrave ™* that something more than the mere presence of patho- 
genic amoebe in the liver is necessary before abscess formation takes 
place. It was shown that the presence of amcebe in the liver, after the 
colon has already become ulcerated, must be of very frequent occurrence. 
When the data brought out in this paper are considered in this con- 
nection, two facts stand out prominently: (a4) Only a comparatively 
small portion of actual ameebic infection of the liver results in abscesses 
or the production of any other changes which we can at this time call 
specific; (b) abscess formation and the bio-chemistry of amcebic lesions 
in general is a complex phenomenon not yet fully elucidated. Prob- 
ably it depends, ,at least partially, upon related alterations which occur 
both in the parasites and in the involved tissues. 
VI. SUMMARY. 
In comparing our observations with some of the recent literature upon 
the biology of amaebe it appears that the establishment of two species 
of amcebx for the human intestine is hardly sustained by the data given. 
While the multiplicity of species of amcebe inhabiting the human 
intestine is not questioned, it is found by working with cultures of pure 
species, grown from a single amoeba, that variations in some of the charac- 
teristics are as great,as are many of those given by some authors for 
species determination. 
We have not actually observed the entire life cyele of any ameeba, but 
known forms of reproduction are: (1) Simple fission and less frequently 
budding during the vegetative stage, and (2) one or more forms of 
reproduction from an encysted stage either by some type of sporulation, 
sporogony, or schizogony or by a phenomenon which has been observed 
in cultures, namely, the escape of a single amceba from a ruptured cyst. 
The size of individuals of pure species of amcebe in culture varies with 
the age and environment of the parasite. In the same plate culture all 
ages and sizes are found in the vegetative stage. In naturally encysted 
% Phil. Journ. Science (1906), 1, 552, 553. 
