3*8 



PHYSIOLOGICAL CHEMISTRY 



refers to the mystery of the useless secretion. Basch 1 has recently sug- 

 gested that this secretion of "witches milk" is brought about by the 

 passage of hormones (see Chapter on Pancreatic Digestion) from the 

 blood of the mother to the fetus. 



Lactose, the principal carbohydrate constituent of milk, is an impor- 

 tant member of the disaccharide group. It occurs only in milk, except 

 as it is found in the urine of women during pregnancy, during the nurs- 

 ing period, and soon after weaning; it also occurs in the urine of normal 

 persons after the ingestion of a very large amount of lactose in the food. 

 It is not derived directly from the blood, but is a specific product of the 

 cellular activity of the mammary gland. It has strong reducing power, 

 is dextro-rotatory and forms an osazone with phenylhydrazine. Lac- 

 tose is not fermentable by pure yeast. For changes which lactose 



FIG. 104. LACTOSE. 



undergoes in lactic acid fermentation see page 314. The crystalline 

 form of lactose is shown in Fig. 104. 



Casein, the principal protein constituent of milk, belongs to the 

 group of phosphoproteins and contains 0.7 per cent of phosphorus. 2 

 It has acidic properties and combines with bases to produce salts. 3 

 It is probably present in milk in the form of neutral calcium casemate 

 (Casein Ca^.. 4 It is not coagulable upon boiling and is precipitated 

 from its neutral solution by certain metallic salts as well as upon satu- 

 ration with sodium chloride or magnesium sulphate. Its acid solu- 

 tion is precipitated by an excess of mineral acid. 



Lactalbumin and lacto-globulin, the protein constituents of milk, 



1 Basch: Munch, med. Woch., 58, 2266, 1911. 



2 Bosworth and Van Slyke: Jour. Biol. Chem., 19, 67, 1914. 



3 Van Slyke and Bosworth: Jour. Biol. Chem., 14, 207-227, 1914. 



4 Van Slyke and Bosworth: Jour. Biol. Chem., 20, 135, 1915. 



