931 
cultures by following simple requirements. Furthermore, it is probable 
that the conditions governing successful changes in symbiosis in artificial 
media are very similar to those taking place in nature and that conclu- 
sions drawn from such changes are sound. If living animals are used 
instead of culture media, alterations in symbiosis within their economy 
are just as apparent as they are in the test tube. It is by changing 
symbiosis that true parasitism, with its far-reaching results, is established. 
However, at ‘present the important point is to show that amoebe of 
various morphologic conditions and from many sources may be deviated 
from saprophytic surroundings to true parasitic environment; it is also 
desirable to determine whether or not this process is reversible. 
(a) Increasing processes——An amceba from water, soil, vegetables, 
animal intestines, or some other source may be cultivated in pure species 
with bacteria, as has-been described in our previous paper. This amoeba 
may then be obtained with a pure culture of bacteria and this bacterial 
symbiosis may be changed at will from time to time. Under certain cir- 
cumstances, previously described cultures of this class may be fed to mon- 
keys or to man, and amoebic infection of the colon result. Such cultures 
may also be injected subcutaneously or into the livers of monkeys, and 
compound amoebic and bacterial abscesses result. The amoebe may again 
be cultivated from both of the above sources. If they are taken from 
the intestine, the original bacterial symbiosis may be satisfactory, but if 
the infection is of several days’ standing then some other bacterium 
from the monkey’s intestine may be necessary. This shows that while 
the symbiosis is still bacterial, it has changed from the one originally 
introduced. The amcebe may also be recultivated from the mixed liver 
abscesses, if the bacteria are still present, but in this case the bacteria. 
which were introduced with the amabe will be found the most satisfac- 
tory symbiotic organism, and usually the only one with which growth 
may be obtained. 
If the liver abscess is allowed to remain undisturbed for some time or 
still better, if the contents of such an abscess is used to produce a second 
one by direct inoculation into another monkey, the cultivation of the 
amcebe becomes more difficult and after a time is rendered impossible, 
notwithstanding the fact that the original symbiotic bacterium may be 
still present in the pus and that this organism is the one used on the 
culture media. 
We therefore conclude from these results that, as in other instances, 
the symbiosis has changed in the liver abscess, and as there are no micro- 
organisms present other than the ones which were introduced, we also 
conclude, and experimentation proves this to be correct, that the change 
in symbiosis in this instance is one which has been formed with the liver 
tissues—that is, represents true parasitism. 
In other words, notwithstanding the fact that the original bacterium 
which was introduced is still présent in the abscess, it is now no longer 
Pee ae 
