426 METABOLISM, NUTRITION, AND DIET 



since it is never completely oxidized within the body, but may be supposed 

 to give rise to a definite amount of urea, not a completely oxidized body. 

 In this case the gram of proteid may be considered to perform the same 

 amount of heat as the proteid would outside the body minus the amount 

 which would be obtained from the complete oxidation of the resulting urea. 



The actual amount of heat produced per diem has been experimentally 

 ascertained in the case of man and animals by the aid of an apparatus, the 

 calorimeter. An animal is enclosed in a metal cage completely contained 

 in a second cage containing water. Air is led into and out of the inner box 

 by means of metal tubes so arranged that the inlet tubes maintain a con- 

 stant temperature and the outlet tubes pass through water between the two 

 chambers. The heat given out by the animal warms the water in the outside 

 box, and may be estimated by the rise of its temperature, the amount of which 

 is known. At the same time the carbon dioxide output is measured. 



The amount of heat evolved by the oxidation of various food stuffs has 

 been carefully measured by numerous observers; the figures calculated by 

 Rubner being perhaps most satisfactory, which are : 



HEAT VALUE TO THE BODY. 



i gram carbohydrate 4.1 Calories 



i " fat 9.3 



i " proteid 4. i 



One gram of dry proteid has a total heat value of 5.754 (Rubner), hence 

 it is obvious that proteid is not completely oxidized by the body. Each 

 gram of proteid yields at least one-third of a gram of urea, which has a heat 

 value of 2.5 Calories per gram. 



Atwater has checked the energy value of the foods actually consumed 

 against the actual liberation of heat and work energy of the human body. 

 He finds a wonderfully close agreement both for periods of rest and for periods 

 of work. Atwater 's estimate for the energy needs of man are summarized 

 as follows: 



Man without muscular work 2,700 Calories 



" with light muscular work 3,ooo " 



" " moderate muscular work 3>5 " 



" " severe " 4,500 " 



The daily output of energy for the adult man is, according to McKendrick, 

 as follows: 



Kilogrammeters. Calories. 



Work of heart per day 88,000 



Work of respiratory muscle 14,000 



Eight hours' active work 213,344 



315,334 or 743 

 Amount of heat produced in 24 hours 1,582,700 or 3,724 



,034 or 4,467 



