18 THE ECONOMICS OF FEEDING HORSES 



The Salts, or Ash, are the mineral or inorganic sub- 

 stances in a food, and consist chiefly of simple com- 

 pounds of sodium, potassium, magnesium, and calcium, 

 with chlorine, carbonic acid, phosphorus, and sulphur. 

 The ash is sometimes called the incombustible part of a 

 foodstuff, in that it is indeed the ash left over after burn- 

 ing the food. The salts do not combine with oxygen in 

 the body, but are excreted in the urine, often in the same 

 form in which they were taken in as part of the food. 

 They therefore supply no heat to the body, and in a 

 certain sense have no nutritive value. At the same 

 time they are essential constituents of a diet, for, as we 

 have seen, the elements of which they are composed are 

 also found in the body tissues, are used up in the 

 chemical activities of the tissues, and therefore must be 

 replaced by salts taken in with food or water. Espe- 

 cially for digestion are salts necessary, as is evident 

 when it is remembered that the gastric juice contains 

 hydrochloric acid, of which the supply must be renewed 

 by the taking in of chlorides, such as sodium chloride 

 (common salt). Again, digestion in the duodenum can 

 only go on in an alkaline medium, due to the presence of 

 sodium carbonate. The blood also can only carry off the 

 waste product, carbon dioxide, as long as it is alkaline 

 from the presence of sodium carbonate. Further, bones, 

 and most of all the tissues, require mineral matter in 

 the food, to the greatest extent during growth, but also 

 throughout life, for the purposes of making good wear 

 and tear. Thus a suitable amount of calcium salts 

 (lime) and phosphates must be present in the food, 

 particularly for young growing animals. 



Whilst it is beyond the scope of this work to enter 

 into the details of the chemical analysis of foods, it may 



