148 BACTERIA, YEASTS, AND MOLDS 



nothing to be desired. It is useful for meats and many 

 other kinds of animal foods. For vegetables and fruits 

 its value is far less, and sometimes very doubtful. For 

 them it should be used only where there is a large quantity 

 of fresh material for which no better method of preserva- 

 tion can be found. 



Use of Low Temperatures 



The value of low temperatures in preserving all forms 

 of food is familiar to every one. Microorganisms are 

 stimulated into active growth by high temperatures and 

 checked by low temperatures. It must be remembered, 

 however, that the temperature at which bacteria grow 

 most readily is not always the same ; for although some 

 species flourish only at warm temperatures, from 70° to 

 100°, others grow best at temperatures only a few degrees 

 above freezing. While, then, a low temperature will check 

 the development of most bacteria, it will not, unless it 

 is actually below freezing, wholly prevent it, since some 

 species grow readily enough at low temperatures. In the 

 consideration of the use of low temperatures, therefore, 

 three phases of the subject may be considered, based 

 upon the degree of cold obtained. 



I. Cold Storage. By cold storage is meant the use of 

 storehouses which are cooled artificially, and where a very 

 low and constant temperature is maintained for months 

 at a time. In some compartments the temperature is 

 held at a few degrees above freezing, while in others 

 it is even below freezing. These low temperatures are 

 commonly produced by the use of artificial-ice machines, 



