500 PHYSIOLOGY. 



temperatures. The increased heat-production on account of the 

 specific dynamic action of the proteid was lost through the increased 

 evaporation of water. 



To determine the energy-value of foods it is necessary to admit 

 that the proteids, fats and carbohydrates undergo complete combustion, 

 the fats producing carbonic acid and water, the proteids carbonic acid, 

 water and urea. The mean value is expressed in calories : 



One gram of fat when burned produces about 9.3 Calories. 

 One gram of proteid when burned produces about 4.1 Calories. 

 One gram of carbo-hydrates when burned produces 4.1 Calories. 

 One gram of alcohol when burned produces 7 Calories. 



One large kilogram calorie equals 100 small calories. The large 

 Calorie is written with a capital C; the small gram calorie with a 

 small c. 



Isodynamic Equivalent. Rubner has shown that the different 

 organic materials for food can replace one another in isodynamic 

 quantities; that is, in quantities which yield equal amounts of calories. 

 The ratio or isodynamic equivalent is as 9.3 to 4.1, or 2.3 to 1. Hence 

 one part of fat can be used instead of 2.3 parts of carbohydrates as 

 sugar. 



From the point of energy- value, 100 grams of fat are equal to 

 about 225 grams of proteids or carbohydrates. In this way we 

 calculate the energy-value of our foods. A great number of analyses 

 have shown that about 10 per cent, of the foods are not absorbed; 

 hence some calories are lost, and must be noted in making up the 

 number of calories needed in making out a diet table. 



In the natural diet of the average man the carbohydrates repre- 

 sent two-thirds of total energy and the other third represents in equal 

 parts the proteids and fats. This division of energy from the three 

 kinds of food is the same for a person who rests or who does work. 

 This is a remarkable fact, and indicates that the organism is able by 

 work to utilize these three kinds of food, 25 per cent, of which energy 

 is transformed into mechanical work, and 75 per cent, of which 

 energy is transformed into heat. 



At different periods of life (1) the proportion of proteid 

 remains nearly constant in the diet; (2) in the nursling the fats in 

 the diet give half the total energy in the nursling, in the infant a third 

 and in the adult a sixth; (3) the carbohydrates furnish a third of 

 the total energy for the nursling, a half for the infant and two-thirds 

 for the adult. 



In order to establish a rational diet for a man we must remember 



