44 THE SECRETIONS: 



SPECIAL CHEMISTRY OF THE MILK. 



Constituents of the Milk, and methods of separating them. 



The following substances are contained in a state of solution 

 in healthy milk : casein, fat (including olein, stearin, butyrin, 

 caproin, and caprin), sugar of milk, extractive matters, and 

 salts. The salts are the chlorides of sodium and potassium ; 

 lactates of potash, soda, probably of ammonia, of lime, and 

 magnesia; phosphates of potash, soda, lime, and magnesia ; and 

 traces of phosphate of peroxide of iron. 



The plans that were formerly proposed for the analysis of 

 milk could not give satisfactory results. For instance, the 

 fatty portion which collects on the surface (the cream) was 

 analysed separately from the poorer fluid beneath it ; by this 

 means, then, were obtained accurate estimates of the two sepa- 

 rate portions, but not of the milk collectively. 



The course adopted by the French chemists, was to evaporate 

 the milk, to take up the butter with alcohol, or a mixture of 

 alcohol and ether, and then to wash out the sugar from the 

 residue; if we reflect, however, that the dried casein of cow's 

 milk is always slightly soluble, and that of woman's milk is 

 freely soluble in water, the source of error in this system be- 

 comes at once obvious. By the adoption of this incorrect 

 method, Payen fixed the amount of casein at O23, while the 

 mean of seventeen analyses performed by myself yielded 3'4, 

 or more than fourteen times as much. 



The following is the method that I adopt :* a known quan- 

 tity of milk is evaporated to dryness, and the residue weighed; 

 by this means we determine the amount of water. A weighed 

 portion of the dried and finely-powdered residue is thrice ex- 

 tracted with five or six times its volume of boiling sulphuric 

 ether, in order to remove the fat. After the removal of the 

 fat, the residue is placed in a porcelain basin, is again pulverized, 

 and digested with a little warm water. The pulp which is thus 

 formed is treated with an additional quantity of boiling water, 

 in which it is partially soluble if the analysis is being conducted 



1 Die Frauenmilch nach ihrem cheraischen imd physiologischen Verhalten, p. 27. 



