DEATH TEMPERATURE I29 



forms. One is the active, growing form, in which they 

 feed and multiply rapidly ; the other is the spore form, in 

 which they are at rest, neither feeding nor growing. In 

 the former condition they are easily killed by moderate 

 heat, a temperature of 140° to 160°, if continued an hour 

 (usually a much shorter time), being ordinarily sufficient 

 to destroy them. In the form of spores, however, such a 

 temperature has little value in destroying them. Bacteria 

 can resist without being killed a higher temperature than 

 can any other known form of living matter. Spores of 

 certain bacteria can be boiled for a long time without 

 being killed, and if subsequently cooled they will grow 

 and multiply. To destroy the vitality of such spores 

 requires a temperature above that of boiling water, a 

 temperature rather difficult to obtain, at least for liquids, 

 in an ordinary kitchen. It is, however, important to 

 remember that although many kinds of bacteria spores 

 are not killed by a short boiling, a boiling of a few hours 

 is sufficient to destroy all but the most resistant spores. 

 Any material, therefore, that can be boiled for a consider- 

 able length of time may ordinarily be thus sterilized, that 

 is, may have its actively growing bacteria and their spores 

 destroyed at the same time. This great resistance to 

 heat on the part of bacterial spores is a matter of much 

 importance to the housewife, and she should fully 

 realize it. Canning processes, as we shall see, depend 

 upon the destruction of bacteria, and the resistance of 

 spores to boiling is a factor that should always be 

 remembered, 



A practical lesson to be drawn from these facts is that 

 food heated to boiling in its preparation is thereby, in a 



