256 VETERINARY PHYSIOLOGY 



(3) The Mode of Oxidation. — Every one knows that, at the 

 temperature of the body, proteins, fats, and carbohydrates 

 do not undergo combustion. To bring this about, the 

 action of something comparable to an enzyme with an 

 activator is necessary. 



The enzyme-like substance appears to be formed, possibly 

 from the lipoids of the protoplasm, by an auto-oxidation by 

 which a peroxide is formed, which has a greater power of 

 oxidising than free oxygen has. 



But peroxides alone are not sufficient to bring about the 

 combustion of sugars, lactic acid, etc., an activator is 

 necessary, and such an activator has been prepared from 

 various cells, and, since it activates the peroxide, it has been 

 termed a peroxidase. 



In the oxidation of food-stuffs in muscle and other 

 protoplasm the following steps seem necessary : — First, the 

 formation of a peroxide in which oxygen is stored at a high 

 Dotential ; second, the activating action of a peroxidase. 

 These together may be called an oxydase. 



(4) Energy Value of Proteins, Fats, and Carbohydrates.— To de- 

 termine the amount of energy yielded by the oxidation 

 of each, all that i.-:- necessary is to find the amount of heat 

 evolved by its combustion. This is done by burning a known 

 weight in a water calorimeter, an apparatus by which all the 

 heat evolved is used to heat a known volume of water. The 

 Bomb Calorimeter is generally used for this purpose. It consists 

 of a thick metal case in which a weighed quantity of the food 

 to be investigated can be placed in oxygen. By means of 

 wires it can be completely burned by an electric spark. 

 The metal case is placed in a known quantity of water and 

 the heat given off from the food goes to heat this water. By 

 taking the temperature before and after the combustion the 

 amount of energy in heat units, or calories, may be calculated. 

 Suppose that 1 gram of starch was put in the bomb calorimeter 

 and the case then placed in 1 litre, i.e. 1 kilogram of water : 

 suppose the temperature of the water was raised 4-1^ C, this 

 would mean that 1 gram of starch had liberated 4-1 Calories 

 of energy. 



It is known that, in the normal individual, fats and 



