Human Nutrition. 761 



less food is needed than in cold ones, ami in summer the food require- 

 ment is somewhat lower than in winter. 



From scientific experiments an approximate measure has been made 

 of the amount of energy spent by the body in its daily activities, at rest 

 or at work, asleej) or awake. If tlie energy value of the food is know'n, 

 it is possible to form some idea of how much fo(xl to supply. There can 

 be, however, no accurate standard which will apply to all persons, for 

 the human machine has too much individuality to permit that. If a 

 statement is made concerning the food requirement of a grown person 

 it must be kept in mind that there may be a dozen reasons why the 

 given amount may be too much for one person and too little for another. 

 Any food standard that is given, may be accepted as a guide, but not 

 as a hard and fast rule, and must be used with good common sense. 



The following table gives the result of some experiments made to 

 determine the hourly and daily expenditure of energy of the average 

 normal grown person when asleep and awake, at work or at rest. 



Average Normal Output of Heat From the Body 



Conditions of Muscular Activity 



Man at rest, sleeping 



Man at rest, awake, sitting up 



Man at light muscular exercise 



Man at moderately active muscular exercise . 



Man at severe muscular exercise 



Man at very severe muscular exercise 



Average 



Calories 

 per hour 



65 calories 

 100 " 

 170 " 

 290 " 



450 " 



600 " 



The internal activities of the body go on constantly, the heart must 

 beat, respiration must continue, the blood must circulate and carry 

 food to the cells and remove waste products from them, hence, even in 

 sleep there is a constant spending of about 65 calories an hour. Any 

 restlessness or uneasiness increases this expenditure. Exi)eriments 

 on animals have proved that the animal which has clean quarters and 

 comfortable bedding is decidedly less expensive to feed, for its rest is 

 so much more comi)lete during quiet easy sleep that it uses up less 

 material. These facts are also true for the human being, and restless 

 sleep and nervous work raise the food requirement. 



The above figures show in a clear way how very greatly hard work 

 may increase the food requirement. Compare the expenditure of 170 



