158 NUTRITIONAL PHYSIOLOGY 



that amino-acids uncombined may escape the influence of 

 the liver, and be taken to all parts of the body and offered 

 in free condition to organs which may require them. If 

 this is the usual procedure the suggestion is that the blood 

 proteins form a rather stable reserve mass of food material 

 not much subject to depletion and renewal under ordinary 

 conditions of feeding. In starvation we know that the pro- 

 teins of certain organs are used to keep up the nutrition of 

 others more essential to survival. It would be interesting 

 to know whether such transferred material is carried in the 

 form of amino-acids or organized temporarily into proteins 

 of the type found in the plasma. But there is no part of 

 physiologic chemistry where our knowledge is so much at 

 fault as just this section. 



A SUMMARY OF METABOLISM 



Fats are hydrolyzed in the alimentary canal to fatty 

 acids and glycerin. To an uncertain extent there is soap 

 formation. These products are largely recombined to 

 form fat during the passage through the lining cells of the 

 intestine. Fat is stored chiefly in adipose tissue. Its 

 eventual service is to be oxidized to carbon dioxid and 

 water with release of its energy. 



Carbohydrates enter the circulation in the form of simple 

 sugars, mainly glucose. There is little sugar in the blood 

 at any one time. Much is dehydrated by the cells of the 

 liver and muscles to make glycogen, subject to reconversion 

 to sugar when required. A surplus may be converted to 

 fat. The possibility of the converse change from fat to 

 sugar is generally held to be unproved. The final value 

 of carbohydrate is like that of fat; its energy is set free 

 through the respiratory oxidation, and the end-products 

 again are carbon dioxid and water. The internal secretion 

 of the pancreas is necessary to bring about this destruction. 



Proteins are hydrolyzed to simple compounds (amino- 

 acids or combinations of these), and these are used for the 

 synthesis of the new proteins of types peculiar to the 

 species which can be utilized for growth or repair. A 



