16
Scientific Memoirs by
surface of the medium with a thick, continuous stratum of growth, tubes con-
taining ζ, θ and ι show at utmost mere traces of growth around the orifice of
the needle-track. In the case of θ and ι this retarded development is invariably
associated with extreme modification of morphological character in the consti-
tuent elements, which lose all resemblance to comma-bacilli and appear in the
form of circular or oval cocci, solitary or associated in pairs (Plate IV, Figs. 5, 6).
In the case of ζ a similar modification is sometimes present, but in many instances
many of the elements retain a bacillar form only deviating from the normal in
deficiency of curvature (Plate IV, Fig. 4). There can be no question that in
the case of many forms cultivation on non-neutralised agar-agar media is
associated with conspicuous morphological modification tending to abbreviation
and diminished curvature in the elements which, where pushed far enough, leads
to the substitution of coccoid for bacillar forms. Complete substitution only
occurs in cases where the medium is very uncongenial and growth proportion-
ately retarded, but the modification is not solely regulated by this as we find
the growths of formζ w h i c h a s a r u l e a r e e v e n m o r e r e t a r d e d t h a n t h o s e o f
θ and ι, frequently containing a majority of unequivocal bacillar elements, whilst
those of the other two forms are purely or almost purely of a coccoid character,
and, on the other hand, among the forms which grow with the greatest readi-
ness on non-neutralised media there is one at all events, form e, in which the
morphological modification is invariably highly developed.
In those cases in which complete morphological modification has occurred,
the elements in growths of form c are generally readily distinguishable on
account of their relatively large size (Plate IV, Fig. 6), but those in growths of ζ
and θ are practically indistinguishable in spite of the marked differences which
their elements present when developed in neutralised media.
A phenomenon of this nature very clearly indicates the importance of
avoiding comparisons of the characters of unhealthy, more or less abortive
growths in any attempt at deciding the question of the presence or absence of
specific differences between the organisms which produce them. Just as in the
case of unhealthy and abortive growths on potatoes we find the characteristic and
distinctive features presented by vigorous, healthy growths of the various forms
of choleraic comma-bacilli diminishing proportionately with the increase in the
abortive character of the development and in extreme cases practically disap-
pearing, so in the above instance we have a disappearance of the morphological
distinctions presented by the constituent elements of vigorous growths in neu-
tralised agar-agar media in the abortive growths in non-neutralised ones. When
we compare the elements of forms ζ a n d
θ in vigorous growths in neutralised agar-
agar media or their general habits of growth when growing freely in neutralised
common gelatine media, we cannot doubt that they indicate the presence of
essential differences in nature, but were we to confine ourselves to the phenome-
na presenting themselves in the unhealthy and etarded growths occurring