FATE OF THE FOOD ABSOKBED 387 



training, where the muscles may be enormously increased by 

 the building up of the protein-derivatives of the food into their 

 protoplasm. 



C. Carbohydrates are stored to a small extent in the liver and 

 in the muscle. 



III. THE LIVER IN RELATIONSHIP TO ABSORBED FOOD 

 AND TO THE GENERAL METABOLISM 



The liver develops as a couple of diverticula from the 

 embryonic gut, and is thus primarily a digestive gland, and 

 in invertebrates it remains as a part of the intestine both 

 structurally and functionally. But in mammals, early in foetal 

 life, it comes to have important relationships with the blood 

 going to nourish the body from the placenta (see p. 440). The 

 vein bringing the blood from the mother breaks up into a series 

 of capillaries in the young liver, and in these capillaries the 

 development of the cells of the blood goes on for a considerable 

 time. Soon the liver begins to secrete bile, while animal starch 

 and fat begin to accumulate in its cells. Gradually the forma- 

 tion of blood cells stops, and the mass of liver cells become larger 

 in proportion to the capillaries. As the foetal intestine develops, 

 the vein bringing blood from it the portal vein opens into 

 the capillary network of the liver, so that, when at birth the 

 supply of nourishment from the placenta is stopped, the liver 

 is still associated with the blood bringing nutrient material to 

 the tissues. 



1. Relation to Carbohydrates Glyeogenie Function. Claude 

 Bernard discovered that sugar is formed in the liver. This 

 formation of sugar goes on throughout life, and on account of 

 this constant supply the amount of sugar in the blood does 

 not diminish, even when an animal undergoes a prolonged fast. 

 In starvation there are only two possible sources of this 

 glucose the fats and the proteins of the tissues. There is no 

 conclusive evidence that fats can be changed to sugar in the 

 liver, although it is difficult to explain the large amount of 

 sugar which is sometimes excreted in phloridzin poisoning, 

 unless it is formed from fats. That it is not all formed from 

 proteins is shown by the fact that the sugar which appears is 

 sometimes greater than could be produced by the proteins broken 

 down, as indicated by the output of nitrogen. 



