272 ANATOMY AND PHYSIOLOGY 



energy, by entering into the up-building of the tissues which are 

 quickly used up for those purposes ; while the proteins have in addi- 

 tion as their principal function, the construction of body tissues of a 

 more permanent character. 



These changes are largely dependent upon the combination of 

 oxygen with food or tissue compounds. "The essential source 

 of heat and mechanical work developed in the animal organism 

 is to be found in the oxidations" (Hammarsten). But behind 

 these are the enzymes; in nearly all active tissue cells the changes 

 begin with their action. Certain oxidizing ferments make the 

 first splitting of complex substances, afterward the union with 

 oxygen follows. 



In digestion processes we have seen that the first change is 

 associated with a splitting of and union with the elements of water 

 (H 2 0). The enzymes which set this change in motion are hydro- 

 lytic enzymes. 



FOOD VALUES 



By study and experiment it is found that the proper propor- 

 tions of proteins, carbohydrates and fats in the human dietary are 

 as follows: proteins one-fifth, fats one-fifth, carbohydrates 

 three-fifths. Since in the body, heat and mechanical work are 

 produced in company, the degree of heat evolved by work is taken 

 as the measure of force to be supplied by food, or the measures of 

 food value. 



The heat unit of measurement is called the calorie (large 

 calorie), which signifies the amount of heat required to raise one 

 kilo of water to iC. 



A food which when burned will do this has a calorific value of 

 one degree, that is, it is graded at one calorie in value. 



The following are estimated averages of calorific values. 



Proteins one gram yields 4 . to 4. i calories. 



Carbohydrates one gram yields 4.1 calories. 



Fat one gram yields 9 . 3 calories. 



The average working man of 20 kilos weight, needs a ration of 30-40 

 calories for each kilo. 



The average resting man of 20 kilos weight, needs 30 cal. per kilo. 

 The average sleeping man of 20 kilos weight, needs 25 cal. per kilo. 



Upon the basis of calorific values various diet tables have been 



