702 PHYSIOLOGICAL CHEMISTRY. 



arranged for small quantities, is manufactured for the examination of human 

 milk. 



c. Total protein. Separate the skimmed milk from the cream of the sample 

 under observation. Dilute the skimmed milk with 4 parts of water and with 

 this solution fill Esbach's albuminometer (see Index) to the mark U, add 

 Esbach's reagent to R, and allow to stand 24 hours. Multiply the reading by 

 5; the result gives the number of grammes per liter. Skimmed milk is used 

 in order to avoid the fat which would be carried down with the protein if 

 whole milk were used. 



d. Albumin and globulin. Dilute 25 c.c. of milk with 15 c.c. of water in a 50 

 c.c. flask, heat on a water-bath to 38 to 40 C. (100 to 104 F.), and add very 

 gradually a saturated solution of potassium alum until a rapidly subsiding 

 coagulum of casein forms. Add water to make 50 c.c., filter, and estimate the 

 simple proteins (albumin and globulin) in the filtrate by means of the albu- 

 minometer, as above, multiplying the reading on the instrument by 2. Another 

 method for the estimation of total protein or of the simple protein depends on 

 the accurate determination of nitrogen in milk or in milk after the removal of 

 casein. The percentage of nitrogen multiplied by 6.25 gives the percentage of 

 protein.) 



e. Determination of milk-sugar. Lactose can be estimated by titration with 

 Fehling's solution ; for details of the operation see chapter on Urine-analysis. 

 A second method depends on the rotatory power of lactose : milk is freed from 

 protein and then examined by the polarimeter. 



/. Determine total solids, as well as all other constituents, by following the 

 directions given above. 



Human milk. The quantitative differences between human milk 

 and cows' milk have been shown in the table on page 695 ; they con- 

 sist chiefly in this, that human milk contains only about one-half the 

 quantity of protein and of inorganic salts, but one-third more of 

 lactose, as compared with cows' milk. In addition, it may be said 

 that human milk is richer in lecithin ; moreover, the proteins of 

 human milk differ from those of cows' milk. When human milk 

 is treated with acids or rennin, casein or paracasein is formed less 

 readily than by treating cows' milk in the same way. The precipi- 

 tates show marked physical differences from one another. Casein 

 from human milk is easily and completely soluble in gastric juice, 

 and human paracasein is precipitated in a loose and flocculent form, 

 which is much more readily digested than the tough and more 

 compact masses from cows' milk. The casein of human milk shows 

 a lower percentage of carbon, nitrogen, and phosphorus, but a higher 

 percentage of hydrogen, sulphur, and oxygen, than casein of cows' 

 milk. Finally, opalisin, a protein rich in sulphur, is found in human 

 milk exclusively. 



Modified milk, used for infant feeding, is cows' milk, the composition of 

 which has been changed so as to resemble that of human milk. The quantity 



