220 



PHYSIOLOGICAL CHEMISTRY. 



lowing table which was compiled mainly from the results of inves- 

 tigations by Bunge and by Abderhalden. It will be noted that the 

 composition of the milk varies directly with the length of time 

 needed for the young of the particular species to double in weight. 



Lactose, the principal carbohydrate constituent of milk, is an 

 important member of the disaccharide group. It occurs only in 



FIG. 75. 



LACTOSE. 



milk, except as it is found in the urine of women during preg- 

 nancy, during the nursing 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. The souring 

 of milk is due to the formation of lactic acid from lactose through 



