THERMOPHORE. 171 



allowed to stand. As the apparatus cools the acetate of 

 sodium solidifies at about 58 C., and in solidifying it gives 

 off its heat to the milk within the inner chamber. The milk 

 may be kept by this means at a temperature of from 40 to 

 55 C. for ten hours. It might be expected that at such high 

 temperatures the bacteria would grow very fast, but this is 

 not found to be true. On the contrary, the bacteria begin 

 to disappear and, after several hours, are perhaps less numer- 

 ous than at first. If two samples of the same milk are placed, 

 one in an ice chest and the other in the thermophore, at the 

 end of ten hours the sample in the thermophore will contain 

 the smaller number of bacteria. 



The chief advantage of the thermophore is that it is a con- 

 venient device for keeping milk warm. In feeding young 

 children with milk it is necessary to warm the milk and this 

 is a great inconvenience, especially during the night. The 

 thermophore keeps the milk warm for ten hours, and at the 

 same time prevents the growth of bacteria. The device is, 

 however, so new and so little is known about it that it is 

 impossible at present to say whether or not it will really 

 prove a practical means of treating milk. It is not yet upon 

 the American market. 



Use of Ice. Nothing has as yet proved of such practical 

 value in preventing the growth of bacteria as the use of low 

 temperatures. Different localities, however, differ much in 

 their methods of the use of cold. In this country there has 

 been a very wide adoption of the use of ice for the purpose of 

 keeping milk cool during transportation. This has resulted 

 in the invention of the ice car, in which the milk is kept sur- 

 rounded by ice, making it possible to retain the milk for 

 two days before distribution, and yet furnishing the con- 

 sumer with milk which has comparatively few bacteria and 

 keeps well. This is easy to understand, since, as shown in 

 Chapter IV., at a temperature of 50 F. the bacteria hardly 

 multiply at all for nearly forty hours, and for fifty hours 



