VARIETY IN FOOD. 107 



fact that the fodder habitually consumed is not sufficient for 

 the requirements of the system. In this case, the condition of 

 the food its being too dry, too hard, or too moist or the 

 proportion or number of its constituents or elements will pro- 

 bably be at fault ; for in health, the nearer the food is to 

 perfection, the less will be the desire for change. Thus we 

 find that the craving for vegetable food evinced by a foal 

 increases with age ; and that many species of animals live 

 almost exclusively on one particular kind of diet. Although 

 the horse in a state of nature might appear to be a one-food 

 (a solely grass-feeding) animal, grasses differ from each other 

 in their nature and composition. A study of the tables on 

 pages 62 and 63 shows that deficiency of constituents in one 

 food may be supplied by feeding on other foods. As regards 

 the food of the horse, the transition from a state of nature 

 to life under civilised conditions is chiefly one from green 

 food to dry food, and from food poor in nitrogenous matter 

 to one rich in that constituent. The means for remedying 

 any ill effects to health from such a transition are self- 

 evident. It goes almost without saying that, as a rule, the 

 less the desire shown by a horse to change his food, the more 

 suitable will it be to meet his requirements, supposing that 

 he is in strong work. 



COMPARATIVE NUTRITIVE VALUES OF DIFFERENT FOODS. 



Supposing that a horse has a full supply of water and 

 oxygen, we may regard the nitrogenous matter, carbo- 

 hydrates, fat, and mineral matter of his food as its nutritive 

 constituents. If when comparing two foods, we find that each 

 of them is richer than the other in different constituents, it 

 will be impossible for us to say which has the higher nutritive 

 value ; because these respective constituents have their own 

 special work to perform, and their importance to the body 

 varies according to circumstances, such as those of work, age 



