192 
PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
hay-infusion which had been completely sterilized by eight hours’ boiling. When 
infected, the infusion was brightly transparent, but forty-eight hours after its infection 
it Avas teeming with Bacteria. With regard to the doctrine that these organisms arise 
from “ dead organic particles,” irfstead of from living germs *, no scientific man at the 
present day ought, I submit, to be called upon to spend a moment’s thought upon it. 
One other reference will suffice. I have had bundles of hay hung up for seven or 
eight weeks in the hot rooms of the Turkish Bath in Jermyn Street, and exposed during 
the whole of this time to a temperature of 140° and upwards. The germs adherent 
to this hay were not killed by even this amount of desiccation. When a sterilized 
animal or vegetable infusion was infected with them they gave birth in the usual time 
to swarms of Bacteria. 
§ 22. Sterilization by discontinuous Heating. 
Keeping the distinction between germs and developed organisms here insisted on, and 
the probable changes that occur in passing from the one to the other, clearly in view, I 
have been able to sterilize with infallible certainty the most obstinate infusions referred 
to in this paper ; and this has been accomplished without either raising the temperature 
of the infusions beyond their ordinary boiling-point, or inordinately prolonging the 
application of heat. The infusions may be sterilized by a temperature even below that 
of boiling water, while the time of its application may be but a minute fraction of that 
resorted to in some of the foregoing experiments. 
It is an undisputed fact that active Bacteria are killed by a temperature far below 
that of boiling water. It is also a fact that a certain period, which I have called the 
period of latency, is necessary to enable the hardy and resistant germ to pass into that 
organic condition in which it is so sensitive to heat. There can hardly be a doubt that the 
nearer the germ approaches the moment when it is to emerge as the finished organism, 
the more susceptible it is to that influence by which that organism is so readily 
destroyed. We may learn from experience, aided by the power of search which the 
concentrated luminous beam places in our hands, what is the approximate time 
required for the Bacterial germ to pass into the Bacterium. Say that it is twenty-four 
hours. Supposing the heat of boiling water, or even a lower heat than that of 
boiling water, to be applied to the germ immediately before its final development, when 
all its parts are plastic, when it is, in short, on the point of reaching a stage at which 
a temperature of 140° Fahr. is demonstrably fatal. It is in the highest degree pro- 
bable that a temperature of 212°, or of 200°, or, indeed, a temperature of 150° if 
applied sufficiently often or for a sufficient length of time, will prove fatal to the germ, 
and prevent the appearance of the still more sensitive organism to which the germ is 
on the point of giving birth. 
Here, at all events, we have a theoretic finger-post pointing out a course which experi- 
ment may profitably pursue. It is not to be expected that the germs with which our 
* ‘ Evolution,’ p. 44. 
