

THERMAL DEATH-POINTS 85 
vital resistance to heat that remains for brief con- 
sideration is as to the death-point of the spores of 
the thermophilic Bacteria, which seem to be the 
most resistant of all. This question has been inves- 
tigated by Christen,’ who arrived at the conclusion 
that the spores of these organisms, commonly found 
in soil, were killed by compressed steam in the 
following periods, when exposed to successively 
higher temperatures :— 
At 100° C. in more than 16 hours. 
OS :-1 10: 2 to 4 hours. 
bls. ‘ 30 to 60 minutes. 
ae Cac oe 5 minutes and longer. 
ios. ~ 1 to 5 minutes. 
ma a a I minute. 
According to Lehmann and Neumann (‘ Prin- 
ciples of Bacteriology,’ 1906, p. 53), from whose 
work I have taken these figures, ‘‘the apparatus 
employed brought the objects to the desired eleva- 
tion of temperature very quickly.” 
These are certainly very remarkable results when 
compared with the very much lower resistance to heat 
shown even by desiccated hay Bacillus germs. But, 
as I have intimated already, the thermophilic soil 
Bacteria are little likely to complicate our results. 
The fact that they are not to be found in tap water, 
and still less in distilled water, enables us practically 
to disregard them as possible contaminations in our 
experiments. We have only to take note of the 
fact that they are perhaps the very lowest forms of 
! Centralblatt fiir Bakteriologie, xvii., p. 498. 
