44 STERILIZATION. 
in the spore condition, say 100° C. for twenty 
minutes. They are then allowed to cool for 
twenty-four hours, and again sterilized as before. 
This is repeated several times. ‘The intermissions 
allow such spores as are present to develop into rods, 
and these are killed by the subsequent heating. 
Pasteurization is the term applied to the partial 
sterilization of milk, effected by subjecting it to a 
temperature sufficiently high to kill all pathogenic 
and most of the souring and spore-forming bacteria, 
but not high enough to produce any physical 
changes, such as are brought about when the milk 
is sterilized. A temperature of 60° C. continued 
for fifteen or twenty minutes is usually sufficient, 
though temperatures as high as 85° C. are fre- 
quently employed. Enhanced keeping qualities 
and the destruction of pathogenic organisms are 
the results of pasteurization. 
The chemical substances most frequently em- 
ployed for sterilization or disinfection ' are solutions 
of corrosive sublimate (1 : 1000), carbolic acid (1:20), 
or formalin (1 : 20). A substance that prevents 
the development of bacteria but does not destroy 
them is an antiseptic. One that destroys all germs 
and spores is a germicide or disinfectant. There 
are many gases, acids, salts, etc., that have anti- 
septic or germicidal properties. 
Bacteria may be remnoved from a liquid by pass- 
ing it through a properly constructed filter of un- 
1 Disinfection is the term applied to sterilization by means 
of chemicals. 
