2 THE ECONOMICS OF FEEDING HORSES 



sufficient to provide an animal with carbon or iron, 

 oxygen or nitrogen, in simple form, for, as such, these 

 substances could not be assimilated. They have to be 

 built up into suitable compounds by plants, and then 

 can be used as food for animals. A plant, by means of 

 the energy it derives from the sun, can take in and 

 assimilate into its own tissues simple inorganic sub- 

 stances such as carbon dioxide and water, or salts such 

 as sodium nitrate, and build them up into complex 

 organic bodies ; but an animal has no such power. The 

 animal requires the finished products of plant activity as 

 its raw material, and can make no use of the simple 

 substances which serve as the food of plants. Further, 

 the higher animals are all warm-blooded, and have a 

 fixed normal body temperature which in health has to be 

 kept up by means of food. For the purposes of animal 

 heat, food may be looked upon as the fuel keeping up the 

 fire ; and just as the heat from a fire may be used to 

 generate steam, which in its turn will do work, so the 

 food supplies energy for the work of the body. Work is 

 being done in the body constantly, whether the animal is 

 asleep or awake, at rest or at work. All the vital pro- 

 cesses—such as the beating of the heart to drive the 

 blood round the circulation, the movements of the chest 

 in breathing, the secreting of digestive juices and other 

 glandular products— entail work being done or energy 

 being expended, and are therefore ultimately dependent 

 on the food. Thus it is all important that the food of 

 an animal shall be adequate in quantity and suitable in 

 kind, and, further, in the case of the horse, where the 

 cost of the food is placed against the animal's earning 

 capacity, it must be arranged as economically as 

 possible. 



