6
Scientific Memoirs by
The question is farther complicated by the fact that characters which
have been acquired under given conditions may sometimes possess a certain
amount of persistence, so that on the transfer of the organism to a different
environment an immediate development of the characters proper to it in the
latter may not occur. It has already been pointed out that the modifications
taking place under the influence, of special conditions have a and that,
this having been reached, the characters of the modified organism remain
more or less stable so long as external conditions remain unchanged ; but,
more than this, continued exposure to unchanged conditions after the limit
of adaptation to these has been attained, in many cases tends in a greater or
less degree either to diminish the capacity for existence, or, at all events, for
rapid modification of characters under altered conditions. When the latter
effect is produced there is not an absolute abolition of liability to modification, but
there appears to be a tendency towards fixation of characters, so that transfer
to a fresh environment, to which another form is proper, does not at once give
rise to the appearance of the latter, but only produces its effect gradually
and by insensible degrees. We thus have two factors at work in influencing
the characters of any organisms such as choleraic comma-bacilli, first, an
inherent tendency to variation under the influence of alterations in environment,
and, secondly, a tendency to increased stability of property in connection with
continued existence under a uniform environment. Under these circumstances
it is evident that the differences which originally present themselves in indivi-
dual specimens derived from distinct sources do not necessarily indicate the
presence of specific differences between them and that it is only as the result
of prolonged and continuous observation of the degree to which differences
continue to exist under the influence of like conditions that we can arrive at
any correct decision of the question. But where we find conspicuous differ-
ences persisting in spite of indefinitely prolonged exposure to the influence of one
environment, and distinct modifications attending transference from one like
environment to another of different nature but also common to the organ-
isms experimented with, the evidence of the existence of specific difference
between the latter becomes overpoweringly strong. It is because I believe
that evidence of such a nature is present in regard to many distinct forms of
choleraic comma-bacilli, and from no ignorance or under-estimate of their
liability to variation that I am led anew to affirm that there is no specific cho-
leraic comma-bacillus, but that the disease may be associated with an indefinite
number of distinct species of such organisms or may exist independent of the
presence of any of them.
The history of the European epidemic of 1892 may be regarded as effectu-
ally disposing of the question whether the comma-bacilli associated with cholera
invariably present the characters which, according to Koch's original statements,
they ought to possess, unless, indeed, we adopt the views of his most enthusiastic