Nutrition. 229 



food of which very little fat exists. It has been suggested 

 that the proteid-sparing action of carbo-hydrates and fats 

 is due to the fact that they are oxidized more readily than 

 albumin, and that they thus prevent the action of oxygen 

 on this body. 



The formation of fat occurs in three ways : (1) From the 

 fat which enters the body, which in the herbivora is small ; 



(2) from the carbonaceous residue of the proteid substances ; 



(3) from the carbo-hydrates of the food. It has been 

 clearly shown by experiment that animals have stored up 

 fat on a purely proteid diet, and, no doubt, the vast quanti- 

 ties of fat found in highty-fed animals, have their origin in 

 the proteid and carbo-hydrate substances of the food. 



Owing to the large amount of carbo-hydrate food used 

 by herbivora, and to the fact that carbo-hydrates require 

 less oxygen for their oxidation than fat, more of the oxygen 

 consumed finds its way back in the C0 2 of the egesta with 

 herbivora than is the case with carnivora, where the greater 

 portion of the oxygen leaves the body combined with 

 hydrogen in the form of water. Herbivora therefore use 

 less oxygen than carnivora, and the respiratory quotient, as 

 seen in the chapter on ' Respiration,' is consequently 

 greater. 



Inorganic Food. — The changes occurring in the inorganic 

 substances of the body are extremely interesting. It is 

 evident that the daily quantity of salts required must 

 depend upon the age of the animal : young growing animals 

 requiring more than adults. 



The remarkable thing about Boussingault's nutrition- 

 tables is, that his animals gave out more salts than they 

 took in with the food. This can only be explained by 

 supposing that the system has the power of storing up 

 inorganic material for future excretion. 



In a special experiment made on a cow to determine the 

 income and expenditure of salts, he found that the animal 

 gave up -205 oz. more silica than it received in the food, 

 but it stored up phosphoric acid and lime. The largest 

 excretion of salts was in the urine the smallest in the milk, 



