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lack of a satisfactory symbiosis or environment for the parasite or to the very 
complex question of tolerance or immunity on the part of the host, exemplified 
in so many ways in other parasitic infections of man, rather than to attribute 
this phenomenon entirely to a lack of pathogenicity on the part of the amoeba. 
In discussing the question of the existence of pathogenic and non- 
pathogenic amebe Schaudinn, as we believe largely owing to false 
premises, has once more gone over the ground covered by the older work- 
ers, which was reviewed in our first publication, and he has again main- 
tained it to be possible to divide amcebe into two types, pathogenic and 
non-pathogenic. 
In the first part of this paper we have noted the zodlogical considera- 
tions upon which he established these two classes, and while we are 
unable entirely to follow his observations, we dislike to take issue with 
that part of his work, and this is particularly the case because, as we 
stated in our previous paper, it is not unlikely that several species of 
amoebe will probably be found to exist in the intestine, and it is also 
probable that more than one species may be found to be concerned in the 
production of lesions in that organ. However, we disagree with the 
classification of “KH. histolytica” and “EF. coli” as being respectively 
pathogenic and non-pathogenic for the following reasons: 
Amebe which may be observed in the stools from patients who have 
no symptoms of diarrhoea or dysentery (the so-called healthy individuals) 
are not confined in their characteristics to those given for “#. colt.” Pro- 
tozoa answering more nearly to Schaudinn’s “Z, histolytica” are surely to 
be isolated from the above class of cases, and probably with almost 
as great frequency as “2. coli.” An amoeba which we have in culture 
(11524 of our first paper) at one time was very virulent, producing 
dysentery when it was ingested by monkeys or man. After about three 
years of cultivation on artificial media, no lesions could for a time be 
produced with this organism, although the exact technique of our first 
inoculations was repeated. This amoeba has again become virulent by the 
manipulations which we have used to produce animal infection with all 
classes of these protozoa. 
It is also true that amcebe answering partially to the description of 
“B. coli” may, and often are, the only ones to be found in the feeces, in 
ulcers, or in sections from some of the most severe cases of the infection 
in man. Cultures of ameebe of this class can be so manipulated as to 
produce amoebic ulceration of the colon in monkeys and in man, and 
furthermore they can be made to produce multiple ameebic abscesses in 
the lungs, liver and omentum after intraperitoneal inoculation. 
One of our ameebe is a very satisfactory type of “H. coli.” It has a 
prominent central nucleus, it is a slowly moving organism, its ectoplasm 
and endoplasm are difficult to differentiate, and in many other char- 
acteristics it conforms to the type. With this organism, which is one 
