492 APPLIED BIOLOGY 



reverse effect of contraction of the arteries and a reduced 

 circulation of blood (see bathing, 458). Also see account of 

 heat regulation by the skin ( 447, 453). 



With the exception of the heart itself and the lungs and 

 brain, the larger organs of the body are well supplied with 

 nerves able to regulate the size of the smaller arteries and 

 consequently the amount of blood-supply. 



Whenever there is a great increase in caliber of the blood- 

 vessels, the heart's beat is increased in order to keep up the 

 pressure. In this way, certain drugs used by physicians 

 may increase the action of the heart by reducing the pres- 

 sure in dilated arteries. 



USE OF FOODS IN THE CELLS 



415. We have now studied the preparation and distribu- 

 tion of foods to the cells. Naturally we now ask questions 

 regarding the use which the cells make of the food supplied 

 to them. In studying the frog, we have noted that foods are 

 used in part for supplying energy and in part for repair and 

 growth. In order to apply this fact to human life we need 

 to consider more carefully the kinds of foods in relation to 

 the supply of energy and materials for repair and growth. 

 Are all foods equally valuable? Should we give any atten- 

 tion to the selection of our daily diet ? Such questions are 

 common nowadays, and show that there is a widespread 

 popular interest in the uses of various foods. We shall first 

 consider foods for energy (especially heat and muscular work), 

 and later, foods for repair and growth. This is only a con- 

 venient division into topics, for some foods can serve all 

 purposes. 



416. Energy and its Conservation. Some general con- 

 siderations regarding energy will make clear the use of foods 

 as a source of power in the human body. 



We are familiar with the fact that stored energy in coal 



