Medical Officers of the Army of India
23
to be followed by complete sterilisation. These phenomena are, no doubt, due
merely to the presence and properties of the spores of the Bacillus. The ex
-
posure to the continued elevation of the water-bath suffices at once to destroy
the vitality, not merely of the developed rods, as brief boiing does, but also that
of all the spores which may simultaneously be present. The precise effect of
mere brief boiling will vary necessarily according to the absence or presence of
spores. Should the medium be exposed to brief boiling at a time when all pre
-
existent spores have germinated, and before a new crop has matured, a single
exposure will be sufficient to secure sterilisation; but, if periods of boiling do not
correspond with periods of absence of spores, the treatment might, of course,
be repeated indefinitely without securing the occurrence of sterilisation. The
tendency to produce spores and the rate with which the process is carried out
in individual cases probably varies, not merely in relation to variations in external
conditions to which the Bacilli are exposed, but also in relation to hereditary
tendencies in the latter themselves, so that even in cases where external condi
-
tions are absolutely alike, a uniform result in respect of amount and rate of spore-
formation need not necessarily present itself. So far as it was possible, the
specimens of milk forming the greater bulk of this series were exposed to ex
-
actly similar conditions, the similarity of thermal ones, at all events, being abso
-
lutely secured by the use of an incubator retained at one steady temperature
throughout, and yet treatment, which at one time of year seemed to be quite
effectual in securing sterilisation, at another entirely failed to do so. That inde
-
finitely repeated exposures of the medium to boiling at relatively brief intervals
should in some cases fail to secure sterilisation, whilst two boilings at wider
intervals secure it in others, must surely be related to presence or absence of
spores. It might at first sight seem that frequent repetition of boiling must
inevitably tell in favour of sterilisation, but, of course, it need not do so unless
the rhythm of the cycle of spore-formation and evolution of Bacilli from the spores
falls in such fashion that periods of boiling and of absence of spores coincide
with one another. Unless this be so, the rapid repetition of the boiling in place
of telling more favourably for sterilisation than less frequent treatment may act in
precisely opposite fashion. A single boiling falling exactly at a time of absence
of spores will serve to secure sterilisation, many repeated boilings, if they do not
coincide with periods of such character, will, of course, fail to do so, and the
very frequency of repetition may secure such want of coincidence.
When, as the result of experiments of the nature of those recorded in the
previous tables, some definite idea of the normal phenomena presenting them
-
selves in specimens of the ordinary milk-supply in Calcutta had been obtained,
a special investigation of the behaviour of Comma-Bacilli in the latter were
carried out. Considerable delay occurred ere these could be initiated, and this,
taking the locality and time of year—Calcutta and the months of May and June—
into account, was noteworthy, seeing that it was caused by the want of a supply