927 
all the flasks, and again, at times, nothing will develop in the flasks inocu- 
lated with bacteria because the symbiotic organism has been lost * in 
working with the mixed cultures. 
CULTURAL SYMBIOSIS. 
In this connection we have little that is new to add to the statements 
made in our first publication. In cultures, as is the case elsewhere, 
excepting in stages in which the amoeba is absolutely parasitic, the 
symbiosis of these protozoa with other living microorganisms is constant 
and definite. 
In mixed cultures of bacteria with amoebe, the symbiosis may easily 
be proved to exist with but one strain of the organisms which are present. 
In some cases, where the amcebee have recently been isolated from extra- 
neous sources, the selectiveness of this symbiosis may not be so marked, 
and again, even from these sources, the association may be so sharp and 
definite that the addition of certain organisms to the culture will destroy 
the amcebe, notwithstanding the fact that an abundance of their sym- 
biotic germs remain in the culture. 
This antagonism of amcebe in culture to certain bacteria was noted 
in our first publication, and has been repeatedly verified since. This 
was first brought out sharply by our discovering that one of our amoebee 
refused to grow in the presence of B. violaceus manile Woolley, no 
matter what its symbiosis was at the time the bacillus was introduced into 
the culture. However, later, by close attention to the methods previously 
described for altering the symbiosis in cultures, this amoeba and B. viola- 
ceus were grown together in pure symbiosis. We have had_ similar 
experiences with several amceebe and with different bacteria since the 
above was published, and in each instance the original, apparently 
marked antipathy between the amoebe and bacteria could be overcome. 
Repeated and carefully controlled experiments have fully demonstrated 
the accuracy of these observations, and in addition have developed some 
interesting points in the character of this altered symbiosis. Both the 
specific character and the property by which amcebe may change their 
symbioses in culture are very important points which, as we shall 
presently prove, have a very suggestive bearing upon the process of 
amoebic infections in animal tissues. 
While a satisfactory association with some living microdrganism seems 
essential to the propagation of amebe in artificial media, it does not 
appear that such organism is used as a food by the parasites, but rather 
that some product of metabolism due to the association, or some enzyme 
produced, is what actually nourishes the ameba. 
In young, healthy cultures of amcebe and any bacterium, the germs, 
upon examination of either fresh or stained specimens, are rarely found 
S That is, it has become overgrown or destroyed in some other way. 
