366 HUMAN PHYSIOLOGY 



within their muscle fibres ; but in mammals such a storage 

 is limited in amount. The salmon also stores surplus proteid 

 material in the muscles, and mammals too appear to do the 

 same. How far a passive storage may occur is not known, 

 but feeding experiments on mammals indicate that only a 

 small amount of proteid can be accumulated. On the other 

 hand, the experience of athletic training shows that the 

 muscles may be enormously increased by the building up of 

 the proteid of the food into their protoplasm. Glycogen also 

 is stored in the muscles. 



3. In the Liver. The liver is a storehouse of carbohydrates 

 and fats (p. 368). Lecithin is always present in the liver, 

 even in prolonged fasting. 



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. But 

 in mammals, early in fcetal life, it comes to have important 

 relationships with the blood going to nourish the body from 

 the placenta. In invertebrates it remains as a part of the 

 intestine both structurally and functionally. The vein bring- 

 ing the blood from the mother breaks up into a series of 

 capillaries in the young liver, and in these capillaries, for a 

 considerable time, the development of the cells of the blood 

 goes on. Soon the liver begins to secrete bile, while animal 

 starch and fat begin to accumulate in its cells. Gradually 

 the formation 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 Glycogenic Function. 

 Claude Bernard discovered that there is a constant forma- 

 tion of sugar in the liver. On account of this constant 

 supply, even when an animal undergoes a prolonged fast, 

 the amount of sugar in the blood does not diminish. In 



