32 ADVANCED PHYSIOLOGY 



same as that of starch (C 6 Hi O5) n , though the two substances 

 have little else in common. Glycogen, too, varies much in the 

 amount stored up when an excess of sugar is eaten, and dis- 

 appears when one is hungry. 



Fats. Tallow, lard, cream, olive oil etc. furnish another 

 fuel that can be burned without giving a nitrogen waste. 

 These fats are derived from both animal and vegetable 

 foods and though made of the same elements as carbohy- 

 drates (C, O and H), they are more complex. Fat is plentiful 

 in the body in both fluid and semi-fluid condition. It is 

 absorbed by the blood from the intestine in a fluid condition, 

 is carried around the body in the blood and is eventually 

 taken from it and deposited in various parts of the body. 



Fat occurs in masses among the muscles and just beneath 

 the skin; it forms a cushion for the eyeballs at the bottom 

 of the eye sockets; it is present among the folds of the 

 intestine; it fills up certain crevices in the exterior of the 

 heart muscle and is deposited in the central marrow of the 

 larger bones. 



Evidence of these facts we have all seen many times in food 

 markets where meats are displayed. No meat is mingled 

 with so much fat as pork; hogs have famously large appe- 

 tites and, at the same time, sluggish habits. A result of this 

 is that only partial use of the fats is made for energy or heat 

 production, thus leaving excessive fat to be stored. A farmer 

 rather easily controls the degree of fatness of horses, cattle, 

 chickens, and other animals by attention to their food and 

 exercise; and their food does not necessarily contain fatty 

 substances, for many animals become fleshy though eating 

 nothing but the proteids and carbohydrates in hay and grain. 



Uses of Carbohydrates and Fats. The body must at all 

 times be kept warm and is constantly using power in 

 muscular activity. Heat and power may roughly be said to 

 constitute energy, and in order to live the body must have not 



I 



