Medical Officers of the Army of India, 15
different times owing to the fact that the extension of the host-bacillus is much
more rapid than that of its guest. The result of this is, that at first the growth
appears to be entirely composed of perfectly straight bacilli of considerable size
and closely resembling the common potato-bacillus, whilst later, minute commas
come to be more and more prominent and widely diffused. This difference in
rate of growth and extension of the two associated organisms renders it possi-
ble easily to obtain pure cultivations of the host-one, without having recourse
to plate-cultures, and simply by inoculation from the peripheral portions of
young growths. Stab tube-cultures in agar-agar inoculated in this way, fail to
show any interstitial growth along the track of the needle, but rapidly yield
pure growths of the straight bacilli on the surface, whilst cultures, taken sub
-sequently and after the comma-bacilli have had time to diffuse themselves,
yield surface growths consisting of a mixture of the straight bacilli and commas,
and abundant, interstitial, softly clouded growths of commas alone. After pure
cultivations of the host-organism had been obtained in this way, an indefinite
series of cultures on agar-agar or on potatoes could readily be conducted,
whereas, whenever pure cultures of the commas were obtained, an indefinite
series of agar-agar sub-cultures were easily carried out, but growth on potatoes
could only be secured by means of artificial association of the two organisms.
Subsequent experiments, in which the common potato-bacillus was em
- p l o y e d a s a h o s t i n p l a c e o f t h e h o s t - s p e c i e s j u s t d e s c r i b e d , s h o w e d t h a t t h e
former also possessed, although in minor degree, the power of favouring the
growth of the comma-bacillus on potatoes, and, in the case of another species
of comma, Sarcina lutea showed unequivocal evidence of playing a similar part.
The precise method in which the host schizomycetes act in favouring the
growth of their associates has not meanwhile been definitely determined, but it
appears not improbable that, in cases such as the present, their action may to
some extent depend upon their effecting alterations in the reaction of the
basis, for whilst the reaction of the surfaces of uncontaminated potatoes is nor
- m a l l y d e c i d e d l y a c i d , t h a t o f p o t a t o e s i n v a d e d b y t h e c o m m o n p o t a t o - b a c i l l u s
is only faintly acid, and that of those affected by the other host-species is faintly
alkaline.
Whatever the precise method of action may have been, there can, at all events,
be no question, that, in the above phenomena we have conclusive evidence of the
fact that an association of choleraic comma-bacilli with certain schizomycetes of
totally different nature may play an important part in determining the continued
vitality and multiplication of the former. So far, then, as comma-bacilli, or, in other
words, certain species of vibrionic organisms, are in any way causally related to
cholera, it is clear that one of the factors favouring the evolution of the disease in
any locality may be the presence of certain other schizomycetes in the latter, or,
in other words, that these adjuvant species may be a factor in determining what
Von. Pettenkofer has denominated " local predisposition." It matters not whether