Medical Officers of the Army of India.
Potato-cultivations, where successful, afford much more striking demon-
- s t r a t i o n s o f t h e d i f f e r e n c e s i n p r o p e r t i e s p o s s e s s e d b y t h e d i f f e r e n t s p e c i e s , b u t
unfortunately the success attending them is very variable. In cultivations of
this kind, again, species δ is distinguished from all the others by the readiness
with which it will grow luxuriantly on potatoes of any kind, and by the almost
invariable success which attends transfer of the growth from one potato to
another. In some other species, such as ß,є andζ ,
a c e r t a i n a m o u n t o f
characteristic growth is attainable not unfrequently, but a thorough acclimatisa
- t i o n t o t h e m e d i u m , t o s u c h a n e x t e n t a s t o p e r m i t o f a n y c e r t a i n t y o f s u c c e s s f u l
transfers, takes place only rarely, and in the case of others, such as a, y, θ and i
complete acclimatisation has never shown itself. In the case of the two
remaining species really vigorous growth has never been obtained, and in one
of them, ή , mere traces of growth are all that have ever occurred.
In conducting such a large number of attempts at cultivation on potatoes,
it has been prominently forced on one's attention that it is necessary to exercise
great caution in coming to the conclusion that any species of schizomycete
is incultivable on such media. In them one is not dealing with material of
invariably uniform composition, as may very readily be determined by testing
their re-action. The variations in degree of acidity may in themselves be cap
- able of exerting an important influence on the outcome of attempted cultiva
- t i o n s , a n d t h e y m u s t b e a s s o c i a t e d w i t h t h e p r e s e n c e o f o t h e r d i f f e r e n c e s i n
detail of com positionin the medium which may be equally or more potent in
this respect, so that, ere deciding that any particular organism is incultivable, it
is absolutely necessary that a much larger number of experiments should be
tried than in cases where media of constant composition are dealt with.
One very striking feature in connection with those cases in which thorough
acclimatisation to potatoes as a medium sometimes occurs is the important and
temporarily persistent modification in form and properties of the organism which
accompanies the process. It manifests itself in the highest degree in the case
of species β in which, as has been pointed out, during a period of several
months, a complete incapacity for growth on any other medium save potatoes
was present, and where, even after a partial recovery of the original properties
had occurred, complete recovery of properties and form was delayed for some
time. In some instances, as in certain cultivations of species ε, a complete
re- covery of original properties, as evinced by renewed power for intersticial growth
in Agar-agar media and for the development of the constituents of cholera-purple,
may be regained, whilst the modifications in form continue to be present, and in
other cases, as occurred in certain cultivations of species t, there may be a very
complete recovery of original form without a coincident recovery in properties.
In the latter case temperature appeared to play some part in producing the re
suit, a tendency to resumption of the commatous form being certainly more
frequently present in cultivations which had been kept in the incubator, especially
31