14
potatoes which formed the basis might have been influential, as different samples
of potatoes certainly exhibit very considerable differences in constitution, their
degree of acidity especially, varying very conspicuously. As, however, cultiva-
tions have now been for some time conducted on potatoes of different qualities
without any appreciable alteration in the essential phenomena, it is necessary to
look for some other explanation, and the only factor which presents itself as
l i k e l y t o h a v e p l a y e d a n i mp o r t a n t p a r t i s a t mo s p h e r i c t e mp e r a t u r e .
During the cool period of the early part of 1890 certain features presented
themselves with constancy; as the temperature rose they first became uncertain
in occurrence, and then, for a long time, totally disappeared; when the atmo-
- spheric temperature began to fall considerably, resumption of the original pro
- p e r t i e s b e g a n t o m a n i f e s t i t s e l f , a n d w h e n i t h a d r e g a i n e d t h e l e v e l a t w h i c h
it had been when the series of cultivations was first established, complete re
- s u m p t i o n o c c u r r e d . T h e s e p h e n o m e n a a r e c e r t a i n l y v e r y s t r i k i n g a s s h o w i n g t h e
possibility of the origination of varieties of a considerable degree of permanence,
and perpetuated through very many generations, under the influence of external
conditions, and, as will shortly be shown, they are not peculiar to this species,
but manifested themselves in more or less parallel fashion in regard to other
species also.
Cultivations of this species in broth do not give such strikingly distinctive
specific features as those present in the cultivations which have just been con
- s i d e r e d , b u t t h e y d o s h o w c e r t a i n p e c u l i a r i t i e s(
v i d e
T a b l e I I ) . T h e c l o u d i n g
of the fluid due to the multiplication of the Commas in it diminishes with relative
rapidity, and the surface pellicle has a very great tendency to assume a dry,
membranous, and often permanently wrinkled character. Treatment with acids
gives distinct, and often strong purple, within 24 hours from the commencement
of cultivations exposed to a temperature of from 35° to 37° C. Rapid clearing
of the acidified fluid does not occur so invariably, especially in cultivations of
several days' duration, as in the case of cultivations of the previous species, nor
is there the same tendency as in them to the ultimate development of a brownish
tint in the fluid. Another characteristic of the acidified fluids here is their spe
-
cial tendency to conspicuous effervescence, which frequently persists for a con-
siderable time.
The distinctive features of this species
a r e -
1.
T h e
C o m m a s a r e r e l a t i v e l y s h o r t , t h i c k , w e l l c u r v e d , a n d m o r e o r l e s s p o i n t e d , a n d
they have no special tendency to aggregation into groups.
2. It liquefies gelatine with relative rapidity.
3. The growth over the surface of neutralised Agar-agar media is relatively rapid,
and the stratum which it forms is almost always, within a few days, dryish and rough or
distinctly wrinkled. As in the case of the previous species it is usually incoherent, and,
at the utmost, slightly adhesive.
4. The growth in non-neutralised Agar-agar is relatively rapid.