- Or Tae tee ok a ee 
946 
cultures the size is more nearly uniform in the same plate, but more varia- 
tion is found between two or more different cultures of the same ameeba. 
The color and refractiveness of amcebe are largely an index of environ- 
ment and may be altered in cultures by simple methods. In the stools 
of dysenteric patients such alterations are observed in the changing con- 
ditions of the bowel content. Shape, motility, and pseudopodia forma- 
tion are, at least in part, influenced by physical laws and the environment 
of the. parasite. 
The quantity, refractiveness, and relative distinctiveness of the ecto- 
plasm and endoplasm are of doubtful value in the determination of 
species, and the inclusion of numbers of red blood corpuscles and other 
formed elements by the endoplasm surely is not confined to one species of 
amcebee as classified. 
The shape, location, amount of contained chromatin, of the nucleus 
and the prominence of the nuclear membrane, have been given as 
important points in differentiating between “FH. coli” and “EH. histolytica,” 
but we have not been able fully to confirm the published observations 
nor always to harmonize them with other points in species determination. 
In summarizing this mass of fact and theory concerning the biology of 
amoebe, it is readily seen how difficult it is to systematize the points in 
such a way as to justify classification. We have failed to follow Schau- 
dinn or others in their species determinations, and it appears that many 
important premises upon which their conclusions were based are not 
borne out by our work. It seems to us that more work must be done 
before a satisfactory classification of these protozoa can be made, and 
until such a time we prefer and believe that we are fully justified in 
retaining the name Ameba coli Lésch, to represent those amcebe which 
are found in the intestines of human beings. 
The general plan for the cultivation of amcebe has not been much 
changed from that given in our first publication. 
Amcebe may easily be grown from water, soil, vegetables, and other 
extraneous sources. It is somewhat more difficult to cultivate them from 
the intestine of man or animals, and this is true whether the infection has 
occurred naturally or the parasites have been introduced artificially. 
From liver and other tissue abscesses, whether occurring in the course 
of the intestinal infection or produced by inoculation, growth is still more 
difficult and often impossible. 
Pure cultures of amoebe which will continue to propagate in media free 
from other organisms have not been obtained. This is not due to failure 
to free the cultures from bacteria without injury to the parasites, for 
this may be accomplished with comparative ease. 
Amcebe, outside of certain locations in the human or animal body, 
are always associated with other microérganisms, and experiments demon- 
strate that a more or less definite symbiosis exists between the parasites 
and some one or more of these organisms (usually bacteria). 
a hte” he 
