44 THE MILK QUESTION 



cow's milk (only 0.53 per cent) : much more in woman's 

 milk (1.26 per cent). 



Lactglobulin is the third protein substance which occurs 

 in milk. It is present in very small quantities; in fact, 

 there may be mere traces. 



While normal milk contains very little lactglobulin and 

 small quantities of lactalbumin, colostrum is rich in these 

 two substances, and therefore coagulates when it is heated. 

 Lactglobulin coagulates at 75 C. and is precipitated in the 

 same way as serum globulin, and like serum globulin is 

 insoluble in water, but is soluble to some extent in weak 

 salt solution. 



In the system known as the "percentage method of in- 

 fant feeding" special attention is given to the percentage 

 of the albuminous substances in the milk formula. It is not 

 only comparatively easy to make up formulae containing 

 definite amounts of protein, but the proportion of the vari- 

 ous proteins may also be regulated. Thus it is easy to take 

 out the casein from cow's milk by curdling it with rennin; 

 or the lactalbumin and lactglobulin may be removed thus 

 leaving the casein. In this way various combinations may 

 be arrived at for the baby's good. 



It is not usual to estimate the proteins in a sanitary 

 analysis of milk, since different specimens of milk vary 

 little in this regard, and since there is little inducement for 

 sophistication so far as the proteins are concerned. If we 

 know the weight of the total solids in milk and subtract 

 therefrom the weight of the fat, ash, and sugar, the differ- 

 ence will represent the proteins. This method is sufficiently 

 accurate for ordinary purposes. To estimate the nature 

 of the various proteins requires special skill in organic 

 analysis. 



Inorganic salts 



Milk contains certain definite proportions of inorganic 

 salts, especially the salts of lime, potash, and sodium; also 



