1 70 



Fig. 191 Cross scctiuH uj a calorhiieter. M'l.icie 

 is the food burned''' Of what use is the ther- 

 mometer? The water is stirred by the electric 

 motor. Why is the outside wall of the calo- 

 rimeter so thick? (AMERICAN MUSEUM OF NAT- 

 URAL history) 



grams of water has been raised 10° C by 

 oxidation of the bread, then we know 

 that this sHce of bread contained 1 10 

 Calories of heat energy. 



Measuring energy output in man. There 

 is a device similar to the calorimeter de- 

 scribed above but so large that a person 

 can be placed in it and his heat output 

 measured. This apparatus, however, is 

 so costly that few have been built. In- 

 stead, the amount of heat produced by 

 a person is measured indirectly by meas- 

 uring the amount of carbon dioxide ex- 

 haled or the amount of oxygen inhaled. 

 By making various calculations, includ- 

 ing calculations as to the size and weight 



How a Complex Ayimml Uses Food unit iv 



of the person, physicians can determine 

 a person's heat production. These meas- 

 urements are made when a person has 

 not taken food for some hours and is 

 lying down at complete rest. The heat 

 production under these conditions is as 

 low as it can be; it indicates a person's 

 basal ?netabolisin. Aietabolisin means all 

 the chemical changes that go on in the 

 body. By basal metabolism we mean the 

 amount of metabolism when the body 

 is at rest. But even when the body is at 

 rest there are many active organs. The 

 heart continues to beat, breathing is con- 

 tinued, the digestive organs are doing 

 very little work but have not ceased 

 activity completely, and the brain and 

 some other parts of the body are still 

 doing some work. Besides, oxidation con- 

 tinues in every living cell. 



In men the basal metabolism is some- 

 what higher than in women. It is highest 

 in young babies and grows less through- 

 out life. Naturally as a person becomes 

 more active or exercises, his metabolism 

 increases far above the basal level. In a 

 person living a normal life the actual 

 daily production and use of energy is 

 far above his basal metabolism. This 

 daily production of energy depends 

 upon a person's age, sex, size, weight, 

 t\'pes of activity, and health. 



Calories in your diet. After growth 

 stops, the intake of Calories should equal 

 the output of Calories. If the number of 

 Calories supplied by the diet is larger 

 than the need for energy, the food sup- 

 plying these extra Calories is stored and 

 you put on \\cight. If \ow get fewer 

 Calories than you need, some of the food 

 stored in your body tissues is oxidized 

 and \'ou lose weight. 



