Medical Officers of the Army of India.

5

inluence of the alteration of environment, the resemblance in place of affording
evidence of any true similarity, is strong evidence of essential dissimilarity in
their nature, for it is evidence of the unlike action of like external conditions
upon them.

    Every one is aware that schizomycete organisms generally are readily
modified under the influence of exposure to varied conditions, and, as will
presently be shown, choleraic-bacilli are certainly possessed' of no exceptional
resistance to such action. But the more modifiable any organisms are, the
more have we a right to expect that long-continued exposure to like conditions
must induce an assimilation in the characters of any mere varieties which have
originated as the result of evolution under unlike ones. Now this is most
certainly not the case in regard to many forms of choleraic comma-bacilli.
Certain forms have now been in continuous cultivation in Calcutta under like
conditions for from two to three years and even longer, and although in some
cases and in regard to certain properties they have undergone important
modifications, these have not as a rule given rise to any assimilation of charac-
ters, but on the contrary have merely tended to replace the original differences
by other and even more conspicuous ones. A certain amount of alteration in
character is naturally to be looked for as the result of the continuous cultivation
of modifiable organisms in a new environment. In the present case the
organisms are readily modified, and their rate of multiplication is such that what
for us is a relatively brief period is for them one of geologic duration, so that it
would be surprising indeed did no modifications arise; but, after a time, the
limit of modification for any given environment appears to be reached, and then,
so long as external conditions are unchanged, the acquired characters remain
fixed and stable. When, therefore, we find organisms undergoing modification
and acquiring new characters under the influence of altered conditions, this is
no evidence of any want of specificity in them, of any want of specific differ.
ences between them, unless the modifications which they exhibit are of an
assimilatory character. The differences which they originally presented may
or may not have been of specific value, may or may not have arisen as the
result of antecedent exposure to unlike conditions; but, unless they tend to be
replaced by resemblances under the influence of prolonged exposure to like
conditions, we have no evidence that they are not of specific value.

       In attempting to arrive at any correct decision in regard to the specificity of
such readily modifiable organisms as schizomycetes, we must therefore carefully
avoid regarding mere resemblances apart from the conditions under which they
have arisen as satisfactory guides, for the more any organisms are liable to be
modified by external influences, the greater is the likelihood that modifications
which in one form are induced by one set of conditions may in another be induced
by totally different ones. Mere resemblances are in themselves of no decisive
value; we must have resemblances which have arisen under similar conditions.