14G METABOLISM 



is free from incipient diabetes. Although a small amount of 

 the sugar of the blood may undergo conversion to fat, the 

 greater part is destroyed in all the active tissues of the body, 

 particularly in the muscles and glands. The presence of a 

 glycolytic ferment in the blood is rather doubtful. The most 

 suggestive facts are those obtained by Cohnheim, who showed 

 that the pancreas and muscle have, individually, no or very 

 slight glycolytic power, but when combined have a very great 

 glycolytic power. This is attributed to the activation of a 

 ferment in muscle by a substance derived from the pancreas. 

 The essential value of the pancreas is shown by the production 

 of a permanent glycosuria which follows its extirpation. 



Metabolism of Fats. The greater part, if not all, of the 

 fat undergoing digestion in the alimentary tract is converted 

 into fatty acids and glycerin, and thus is absorbed by the 

 intestinal mucosa. Some of this reappears as neutral fat in 

 the thoracic duct, along which it passes into the blood stream. 

 But it is very soon removed from the circulation. It is very 

 natural to suppose that it is taken up by connective-tissue 

 cells and stored, thus forming adipose tissue; and this, as a 

 matter of fact, is true for a fraction of the fat. This is corrobo- 

 rated by experiments upon dogs in which foreign, easily detected 

 fats, like linseed oil, mutton fat, etc., were fed. But, in addition, 

 body fat is derived from other sources. It is derived from 

 both carbohydrates and proteins. The proof that carbo- 

 hydrates are directly responsible for some of the fat laid down 

 is complete, and, in addition, they act as protein sparers so 

 that the carbonaceous residue of the broken-down protein is 

 shielded from oxidation and laid down as fat. This is inferred 

 from experiments in which the addition of protein to a carbo- 

 hydrate or fat diet, in larger amounts than is just necessary 

 for nitrogenous equilibrium, led to a rapid increase in fat laid 

 on. Although so very probable, absolute proof, qualitatively 

 or quantitatively, of the direct conversion of protein to fat 

 is not obtainable. Sooner or later fat is hydrolyzed and 

 oxidized to carbon dioxide and water, furnishing in this trans- 

 formation the energy which appears as heat, chemical and 

 mechanical work. Many of the tissues of the body contain 

 intracellular, soluble, fat-splitting enzymes, the lipases, inti- 

 mately concerned with fat transformations, 



