1056 The American Naturalist. *  [December, 
or less directly upon some of the more general questions of 
biological importance. As has been before intimated, so little 
direct attention has been given to this subject, that we are 
scarcely able to predict what results may be expected from the 
study of these problems from a bacteriological standpoint. 
But few laws in nature have a wider expression than that 
of variation. In fact, it may be said to be co-extensive with 
life itself. Among the higher complex forms, no two individ- 
uals aré exact counterparts of each other, but as one passes 
from the higher to the lower forms of life, the individual 
differences gradually become obliterated in the more general- 
ized types, and a greater uniformity seems to prevail among 
the different members of the same species. In such simple 
protoplasmic elements as the bacteria, all individual variation 
is concealed, yet, it is presumably present, and were our facili- 
ties for recording such infinitesimal variations, sufficient, we 
would be able to detect structural and functional differences 
in each cell. 
It is too early for us yet to say, whether the evidence that 
bacteriology may yield will be in favor of the “innate ten- 
ency of oe to vary, ” or whether we are to regard 
variation as an “ expression of the influence of environment.” 
An almost untrodden field is before us which lends itself 
readily to experimental conditions and it is highly important 
that we interrogate Nature through the medium of investiga- 
tion upon her more minute, as well as her larger md! of 
life. 
Structural modification expressed either in change of exter- 
-nal form or internal characters is usually made the basis for 
specific differences, so that classifications have been built more 
upon morphological, than upon physiological characters. A 
modification then of characters possessing a morphological 
value would be indicative of a profound change in the consti- 
tution of an organism. How far this would be appreciable in 
the case of bacteria is not definitely settled. A certain amount 
of form variation, (much more in some species than in others) 
is to be seen when different media are used for cultivation. 
Whether these manifestations are merely modifications due to 
