CHAPTER IX 

 FOODS 



The functional activity of every organ and tissue of the body is accom- 

 panied by a more or less active disintegration of the living material, the bio- 

 plasm, of which it is composed, as well as of the food materials circulating 

 in its interstices. The complex molecules of the living material and of the 

 non-living food materials are continually undergoing disruption and falling 

 into less complex and more stable compounds; these, through oxidative 

 processes, are eventually reduced through a series of descending chemic 

 stages to a small number of simpler compounds which, being of no further 

 apparent value to the organism, are eliminated by the various eliminating 

 or excretory organs, the lungs, skin, kidneys, and liver. Among these 

 excreted compounds derived from tissue and from food metabolism the 

 most important are urea, uric acid, and carbon dioxid. Many other com- 

 pounds, organic as well as inorganic, are also eliminated from the body in 

 the various excretions, though they are present in but small amounts. Coin- 

 cident with this metabolic process there is a transformation of potential 

 into kinetic energy, which manifests itself for the most part as heat and 

 mechanic motion. 



In order that the organs and tissues may continue in the performance 

 of their functions, it is essential that they be supplied with nutritive mate- 

 rials simila^ to those which enter into their own composition: viz., proteins, 

 fat, carbohydrates, water, and inorganic salts. These compounds, though 

 originally derived from the food, are immediately derived from the blood 

 as it flows through the capillary blood-vessels. The blood is therefore to be 

 regarded as a reservoir of nutritive material in a condition to be absorbed 

 and transformed into utilizable and living material. Inasmuch as the 

 materials which are lost to the body daily, through processes of disintegra- 

 tion and oxidation, are supplied by the blood, it is evident that this fluid 

 would diminish rapidly in volume, with a corresponding decline in func- 

 tional activity, were it not replenished by the introduction into the body of 

 new material in the food. This is brought about by the sensations of hunger 

 and thirst which periodically arise. 



The Sensations of Hunger and Thirst. For some' time it has been sup- 

 posed that hunger is a general sensation arising in consequence of nutritional 

 changes and referred to the epigastrium. The recent experiments of Can- 

 non, Carlson and others indicate that this is not the case, but that it arises 

 in consequence of a contraction of the musculature of the stomach after its 

 contents have been discharged into the intestine. By reason of the dietetic 

 habits these hunger contractions occur three or four times a day and when 

 once established occur on an average of about once a minute and last for 

 about half a minute. The contractions apparently stimulate nerve endings 

 as a result of which nerve impulses ascend to the cerebrum and evoke the 



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