Nitrogen -free Extract — Carbohydrates 85 



in farm life is that found in milk and which is known 

 in commerce as milk sugar or lactose. The milk of all 

 mammals contains sugar, which appears to be the same 

 compound with every species so far investigated. When 

 fed wholly from the mother, this is the only carbohydrate 

 which young mammals receive in their food. The aver- 

 age proportion of sugar in the milk of domestic animals 

 varies from three to six parts in a hundred, cow's milk 

 containing about five parts. When the cream is removed 

 much the larger part of sugar remains in the skimmed 

 milk, and in cheese-making it is nearly all found in the 

 whej', from which the milk sugar of commerce is ob- 

 tained. Very soon after milk is drawn, unless it is 

 heated to the point of sterilization, or is treated with 

 some antiseptic, the lactose begins to diminish in quan- 

 tity, being converted into lactic acid through the action 

 of germ life. Sour milk, therefore, is different from 

 sweet in at least one compound, and this change causes 

 at least a slight modification of food value. 



CHEMICAL RELATIONS AND CHARACTERISTICS OF 

 THE CARBOHYDRATES 



The various carbohydrates, which have been pre- 

 viously described, are greatly unlike in appearance, 

 taste and other physical qualities, but they are closely 

 related chemically. This is shown not only by what 

 the chemist knows of their constitution, but also by 

 the readiness with which one passes into another, 

 for example, the transformation of starch into dex- 

 trose. Under the influence of certain agencies, such as 



