42 THE MILK QUESTION 



The sugar of milk that is found in the drug store or when 

 bought in commerce, is obtained from whey. It has a 

 slightly sweet taste and is soluble in six parts of cold 

 water. It varies very much in purity. When chemically 

 pure, milk sugar occurs in hard rhombic crystals, but 

 the milk sugar of commerce usually consists of indefinite 

 masses. 



Albuminous matter 



Albuminous matter belongs to a class of chemical sub- 

 stances known as proteins. The proteins all contain 

 nitrogen, and are therefore sometimes called nitrogenous 

 substances. They are one of the essential, if not most 

 important, classes of our food. The proteins build up new 

 tissue and repair waste; they also serve to yield energy in 

 the form of heat and muscular action. A typical example 

 of a protein may be found in the white of egg or the lean 

 of beef. Peas and beans contain proportionately a large 

 amount of protein, while all vegetables, fruits, berries, and 

 cereals contain a certain small proportion. Cow's milk 

 contains about 4.5 per cent of protein substances while 

 woman's milk contains only about 1.5 per cent. The differ- 

 ence is probably due to the fact that the calf matures much 

 more quickly than the infant, and therefore needs more 

 albuminous matter to build new tissue and repair waste. 

 One of the reasons that cow's milk is usually diluted before 

 being fed to infants is to avoid giving an excess of protein. 

 The proteins are usually spoken of as being in solution 

 in milk, but as a matter of fact they are in colloidal 

 suspension; that is, they float as exceedingly small par- 

 ticles or molecular masses in the fluid. 



Of the many different kinds of protein the following are 

 the important ones in milk, namely, casein, lactalbumin, 

 and lactglobulin. A trace of fibrin, mucin, and other pro- 

 teins have also been found. 



Casein is a highly specialized protein found only in the 



