Scientific Memoirs by.
those which have been observed in the case of potato cultivations of any of the
other species.
The growth, in broth-cultivations is often rather slow, clouding occurring
slowly and a pellicle being late in developing. From the beginning broth-culti-
vations invariably gave strong purple on the addition of acids to them within
twenty-four hours from their initiation. Clearing as a rule only takes place slowly
after acidification.
The distinctive features in this species are
—
1. The morphological character of the elements.
2. The phenomena of growth in non-neutralised Agar-agar media.
3. The characters of the growth on potatoes.
It is clearly distinguished by the first of these features from all the other
species save ß and ε, and from them it is defined by the phenomena of growth
in non-neutralised Agar-agar and potatoes, the character of the growth in
gelatine, moreover, being quite different from that in the case of ε .
It will be observed that we may at once divide the species of Comma-Bacilli
which have just been described into two groups. In one of these only a single
species,ζ ’, is included, whilst the other includes the remaining nine species.
The first is characterised by the fact that the elements are incapable of lique
- f y i n g g e l a t i n e , o f i n t e r s t i c i a l g r o w t h i n A g a r - a g a r m e d i a , a n d o f c a u s i n g t h o s e
decompositions in broth which are essential to the development of a purple color
on the addition of acids. In the second group the elements in all cases pos
- sess these powers, although not in like degree in every case. We are according
- l y e n a b l e d t o s u b - d i v i d e t h e g r o u p i n t o t w o s e c t i o n s a c c o r d i n g t o t h e r a t e a t
which the various species are able to liquefy gelatine. When this is done we
have to deal with two secondary groups, in the first of which the rate of liquefac
- t i o n i s c o n s p i c u o u s l y m o r e r a p i d t h a n i n t h e s e c o n d . T h e f i r s t i n c l u d e s f i v e
species a, ß, y, θ and K, the second four species ε,ζ,ŋ and t. Minor differences in
rate distinguish some of the individual species in the sub-groups,—species a & t, for
example, being those which in each group occupy absolutely the lowest place
in this respect, whilst variations in the rate at which liquefaction occurs in
different areas of the medium serve as still further distinctive features in the case
of other species. Neither in regard to absolute rate nor in character of the
process is it possible to distinguish readily between species ß, θ and K, and here
definition can only be obtained by means of characters presented by cultivations
of a different nature, such as potato-cultivations.
Only one species in the large group at all resembles species δ in properties,
and this is i, in which the power of liquefying gelatine is markedly less than
that possessed by any of the other members of the group. The resemblance
lies in the characters of the pellicle formed in broth-cultivations and in the occa-
- sional almost complete absence of the constituents necessary for the develop-
ment of cholera-purple in these.
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