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the amcebe are not reclaimable by culture, even though the exact bac- 
terium which may still be present in the lesions is used for symbiosis, 
and when the strict ameebic lesion free from the bacteria is established 
it is usually impossible to grow the amoebe from it by any of the known 
methods. 
Similar results are obtained in a study of virulence. Just so long as 
it is possible to cultivate an ameba with its associated bacteria, no mat- 
ter how active it may be in animal tissues, its virulence may be decreased 
upon artificial media. 
One of our most virulent amoebe (11524 of our first report), when 
last used at the time that report was written, would, in combination with 
Spr. cholerw, produce very active amoebic lesions. After nearly two 
years of cultivation on artificial media, it was apparently non-virulent 
and, in order to restore it to its original condition, its virulence had 
to be reproduced as in the first instance. Before the restoration of its 
virulence it would not produce lesions in animal tissues; afterwards 
it would. 
This susceptibility of amoebe to a change of environment is of great 
practical importance in its application to naturally contracted amoebic 
infection. If our conclusions are correct, the most dangerous amcebx are 
the ones which live saprophytically in mixed environment, because the 
gastro-intestinal tube is surely rich in bacterial and other organisms and 
amcebe of the kind mentioned above would be the only ones which would 
be likely to form or to find satisfactory symbioses in such a place. Such 
symbioses are necessary and must precede a more parasitic existence. in 
the intestinal lesions. 
It is extremely difficult, to judge from our observations, to understand 
how an amoeba which has once become a strict parasite, or even a very 
selective one in mixed, tissue lesions, can be able to thrive in the mixed 
environment into which it is necessarily thrown upon leaving the body. 
Such amcebe would be extremely dangerous if their transmission were a 
direct one or if the conditions were nearly to approach such a ¢ase; but 
when they are discharged into water, sewage, etc., their tenure of life is 
probably ended, and, while these statements are not proved, it is at least 
possible that in considering prophylaxis in amoebic infection the more 
virulent types derived from lesions in animal tissues are the least to be 
dreaded. 
V. PATHOGENESIS. 
It may be remembered that in our first publication the literature relat- 
ing to the important question of the pathogenesis of amcoebee was summa- 
rized under four headings, as follows: 
(1) Ameebe are harmless; (2) they intensify or alter lesions already present 
(they are secondary invaders); (3) there are pathogenic and non-pathogenic 
amebe; (4) all amoebe are, or may become, pathogenic. 
