METABOLISM, NUTRITION, AND DIET. 435 



above ensued. When they were kept on olive-oil and ivater, all the 

 phenomena produced were the same, except that no ulceration of the 

 cornea took place; the effects were also the same with butter. The ex- 

 periments of Chossat and Letellier prove the same; and in men, the 

 same is shown by the various diseases to which those who consume but 

 little nitrogenous food are liable, and especially by the affection of the 

 cornea which is observed in Hindus feeding almost exclusively on rice. 



The nutritive function of fats and carbohydrates in the body is to 

 serve as a source of energy. They are oxidized, with the ultimate pro- 

 duction of carbon dioxide and water, and must liberate the same amount 

 of energy as when burner! outside the body. A given amount of fat, 

 however, furnishes more energy than a corresponding amount of either 

 proteid or carbohydrate. The stock of fat in the animal body will de- 

 lay the fatal consequences of the deprivation of food. The percentage 

 loss of fat in a starving animal is given on page 440. 



The Formation of Glycogen (Glycogenesis). The important fact that 

 the liver normally forms sugar, or a substance readily convertible into 

 it, was discovered by Claude Bernard in the following way: he fed a 

 dog for seven days with food containing a large quantity of sugar and 

 starch; and, as might be expected, found sugar in both the portal and 

 hepatic blood. But when this dog was fed with meat only, to his sur- 

 prise, sugar was still found in the blood of the hepatic veins. Repeated 

 experiments gave invariably the same result; no sugar being found, 

 under a meat diet, in the portal vein, if care were taken, by applying a 

 ligature on it at the transverse fissure, to prevent reflux of blood from 

 the hepatic venous system. Bernard found sugar also in the substance 

 of the liver. It thus seemed certain that the liver formed sugar, even 

 when, from the absence of saccharine and amyloid matters in the food, 

 none could be brought directly to it from the stomach or intestines. 



Bernard found, subsequently to the before-mentioned experiments, 

 that a liver, removed from the body, and from which all sugar had been 

 completely washed away by injecting a stream of water through its 

 blood-vessels, after the lapse of a few hours contained sugar in abun- 

 dance. This post-mortem production of sugar was a fact which could 

 only be explained on the supposition that the liver contained a substance 

 readily convertible into sugar; and this theory was proved correct by the 

 discovery of a substance in the liver allied to starch, and now generally 

 termed glycogen. 



We may believe that glycogen is first formed and stored in the liver 

 cells, and that the sugar, when present, is the result of its transformation. 



Source of Glycogen. Although, as before mentioned, the greatest 

 amount of glycogen is produced by the liver upon a diet of starch or 

 sugar, a certain quantity is produced upon a proteid diet. The glyco- 

 gen when stored in the liver cells may readily be demonstrated in sec- 



