198 QUARTERLY JOURNAL. 



An examination of the composition of milk will serve to con- 

 firm and to illustrate the preceding remarks. 



When milk is allowed to stand it is found to separate into two 

 partSj the cream which floats on the surface, and a clear fluid un- 

 derneath. This cream consists of globules which may be easily 

 seen by means of the microscope, and are composed of oil. They 

 are mechanically suspended in the milk, and rise to the surface on 

 account of their lesser specific gravity. When heated, or when 

 beaten for a certain time, their envelope is broken and they form 

 butter. 



Milk is thus found to be composed of fat, existing in the state 

 of globules and floating in a thin fluid. This recalls to a certain | 

 extent the composition of the blood. 



If we add to the skimmed milk an acid, it separates into two 

 parts, a coagulum and w^hey. Here again is an analogy with the 

 liquor sanguinis. 



The coagulum is composed of an albuminous matter called 

 casein, the composition of which has already been explained. It 

 is a compound of protein with sulphur. 



The whey is composed of water, holding in solution a kind of 

 sugar, called sugar of milk, and also phosphates and other saline 

 ingredients. 



In milk, we thus find, besides the saline ingredients and water, 

 an oleaginous principle, an albuminous principle and a saccharine 

 principle, that is, the three great staminal principles of the food. 

 The albuminous principle serving as a supporter of nutrition, and 

 the oleaginous and saccharine principles serving as supporters of 

 respiration. 



In butter we have the oleaginous principle separated from the 

 others. In cheese we have the casein united with the butter, as 

 in fat cheese, or separated in a great measure from it, as in skimmed 

 milk cheese. In whey we have the sugar alone with the saline 

 ingredients. 



It was remarked by Prout, before the views of Liebig concerning 

 the nature of the food were published, that milk contained the three 

 great staminal principles of food, and that whatever might be the 

 nature of the food it was necessary that at least two of these prin- 

 ciples should be present in order to support life for any length of 



