tration, p. 115). The baby's parents have already attained their full growth. 

 The amount of food that a person needs to make up for the heat radiated 

 from the surface of the body varies w^ith the size and also w^ith the shape 

 of the body (see illustration opposite). The smaller a child, the more surface 

 he has in proportion to his body weight, and hence he loses relatively more 

 heat. By actual measurement, a one-year-old child needs approximately 

 twice as much energy per pound of body-weight as does an adult. 



Energy needs are indirectly related to sex. Girls and women have a 

 thicker layer of fatty tissue beneath the skin than boys and men. This fat 

 prevents rapid radiation of heat from the body. It is interesting to recall 

 that most long-distance swimming records are held by women rather than 

 by men. Exposure also affects the body's loss of heat. The body loses heat 

 faster in a cold, dry, windy climate than in a warm, moist climate. Cloth- 

 ing and shelter are, of course, factors in the loss of heat. 



Circulation of the blood, breathing, and other processes are continually 

 going on when the body is at rest. "Warm-blooded" animals maintain a 

 constant temperature. The heat continually radiating from the surface is 

 constantly being replaced. Muscular movements are continually taking 

 place in the digestive organs, and energy is used in various other ways 

 within the body. From 40 to 50 per cent of the body is made up of mus- 

 cular tissue. The bulk of this tissue is attached to the skeleton and is used 

 in standing as well as in locomotion and other voluntary actions. At all 

 times, even when these muscles are relaxed, energy is used in keeping them 

 somewhat on the stretch. 



Above the Base Line The amount of energy that the body uses, even 

 while it is "doing nothing", is constantly influenced by two sets of factors. 

 Digesting food involves a measurable amount of energy. Thus the body 

 uses about 6 per cent more energy soon after a meal, when the digestive 

 organs are most active, than just before a meal, when digestion is practi- 

 cally at a standstill. 



When you are sitting and reading, or when you are standing quietly, 

 your body uses about one-and-a-third times as much energy as it does 

 while sleeping. Walking at a moderate pace uses about two-and-a-half 

 times as much; running uses about seven times and stair-climbing about 

 fifteen times as much. 



Unit of Energy To measure the energy expended by the living body, 

 we use a unit developed by engineers. This is the Calorie (Cal), and, like the 

 more familiar foot-pound (ft-lb) used in measuring work, it is composed 

 of two factors. We measure work as if it always consisted of some quantity 

 of matter (pounds) moving a certain distance (feet). In a similar way we 

 measure heat as a quantity of matter, for example, 1 kilogram (kg) of water, 

 being heated a certain "distance" (1 degree on the centigrade scale). 



116 



