929 
Up to this point we have been discussing what might be called sapro- 
phytic or artificial symbiosis in the bowel, and in this connection it makes 
no difference whether the amcebe which are introduced are obtained from 
the head of a cabbage or the ameebic liver abscess of a dysentery patient, 
whether they are “/. coli” or “E#. histolytica,’ and whether they are to 
multiply for a while with their symbiotic bacteria and finally pass out of 
the bowel or whether they are later to develop a true amoebic ulceration. 
(b) Parasitic.—We will now discuss the second type of intestinal sym- 
biosis, which is the connecting link between all which has been brought 
out on this subject and true parasitism or animal tissue symbiosis, which 
is next to be considered. 
In this type, through changing symbiosis and other metamorphoses, 
we reach the condition in which amoebe, instead of multiplying in the 
lumen of a healthy bowel are, by the aid of or association with bacteria, 
growing and propagating in lesions of the intestinal wall, or perhaps, 
while having the same bacterial symbiosis, in liver or other abscesses. 
The exact method by which these changes are brought about is not 
understood any more than are the causes of changes in the virulence of 
bacteria, but that such changes from amebe and bacteria in a normal 
intestine to the same amebe and bacteria in amebic lesions in the bowel 
and elsewhere occur, and finally that this evolution may proceed to. the 
elimination of the bacteria, while amebic lesions are still produced in 
animal tissues, is established beyond the shadow of a doubt. 
We are fully cognizant of the importance of the statement that amcebe 
may change from a saprophytic to a parasitic existence, but after several 
years of careful experimentation we do not see any other interpretation 
of the results. Whether the amcebe in question were ever true sapro- 
phytes may be doubted, but many of them surely came from sources in 
which there was no apparent evidence of present or of past parasitic 
environment, and we have never yet worked with an ameeba which could 
not be changed from a bacterial association to one with an animal tissue. 
There is much in recent literature which bears upon this subject. 
For example, we can quote R. Koch’s explanation of the specificity of 
certain trypanosomata for specific animals, and Theobald Smith’s 
thoughtful communication upon the biology of the tubercle bacillus. 
Smith believes that the parasitism of the tubercle bacillus is best and most 
often developed in the lungs, because, after entrance the tubercle bacillus 
at first has a more or less saprophytic environment in which to propagate, 
and in this way it is able to survive for a sufficient length of time grad- 
ually to take on a more parasitic environment, due to close association 
with the animal tissues. 
Whatever our-interpretations of our findings may be, it is a fact that 
amcebe which probably have been multiplying indefinitely in a bacterial 
symbiosis may: (1) continue indefinitely in such bacterial environment, 
(2) they may change from a bacterial to a mixed bacterial and tissue 
