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930 
symbiosis in the intestine or liver, and (3) this change may be altered to 
true parasitism by the elimination of the bacteria, and tissue invasion and 
destruction by the parasites still take place. 
TRUE PARASITISM. 
We do not frequently find ameebe, without the presence of other liv- 
ing microérganisms, propagating in and associating with definite lesions 
in animal tissues and it is probable that such conditions, when they do 
oceur, are examples of errant types or other unusual circumstances. 
In all intestinal lesions, and in many liver and lung abscesses, there 
are present, in addition to amoebe, one or more varieties of bacteria, and 
cultural experiments demostrate that under these circumstances a definite 
bacterial symbiosis often exists between the amoeba and some of the 
organisms which are present, whereas at the same time the amceba exists 
in partial tissue symbiosis. In other instances, even in mixed ameebic 
and bacterial lesions, the association of the bacteria seems no longer to 
be necessary for the life and action of the amcebe, for no symbiosis with 
any of the bacteria which are present can be found by cultural methods. 
It is probable that, in these cases, the amoebee have taken on a symbiosis 
with the animal tissues; in other words, have become true parasites and 
that. the presence of the bacteria is without significance. 
In naturally acquired amoebic infection in animals, the parasitism 
rarely goes beyond the compound bacterial and amoebic stages referred 
to above. However, true parasitic infections free from bacteria, do 
occur in natural infections and they may be produced artificially. 
Evidences of true parasitism in natural infections are found in bacteria- 
sterile abscesses of the liver, brain and other portions of the body, and in 
two instances, upon which a special report will be made at a later time, we 
have found true amoebic septicemia. In one of these cases the or- 
ganisms were associated with bacteria and P. westermanii in multiple 
abscesses, but in the other no other microérganisms could be cultivated 
from the circulating blood which contained the amcebe. 
In this latter case, amcoebe were found in the blood from the median 
cephalic vein and from the juices of a swollen leg, the swelling of which 
we believe to have been due to amcebic thrombosis. Amoebe were also 
encountered in the small abscesses which developed on the skin of the leg. 
The organisms from the circulating blood remained alive in cultures for 
some time, but would not grow on transplants. 
ALTERATIONS IN SYMBIOSIS. 
It has already been shown, both in our first paper and in this one, 
that satisfactory symbiosis is necessary for the propagation of ameebe 
whether they are in a mud puddle or in an abscess of the liver. It is 
also established that this symbiosis is often a changing one in natural 
surroundings and that variations in environment may be made at will in 
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