ON THE FOOD OF ANIMALS. 301 



to one spot, so far as its rising axis or stem is concerned, its range for supply seems, at first 

 view, extremely limited. As a substitute, however, for the powers of locomotion, its radicles 

 penetrate deeply and widely in search of food, and extend their bounds annually, if its existence 

 is prolonged. The requirements of different plants are various : some require carbonic acid 

 and water only, as those which are composed of cellular tissue, or rather cellulose ; scarcely any 

 exist, however, which are so simple. The boletus and lichen upon our rocks and trees con- 

 tain inorganic matters, and in many there is a free supply of ammonia, as is shown when they 

 decay. 



All the higher animals possess a complex structure, and contain a great variety of elements 

 in combination. To supply these in proper proportions, and adapt them to their periods of 

 growth, to sustain the mature animal and supply its wants, so as to advance our own interests 

 in it, and make it yield to us the greatest service or benefit, is the main object which man has 

 in keeping the domesticated animals. To accomplish this end requires an intimate acquaintance 

 with the various kinds of food, and with the physiology or nature of the animal, and of the per- 

 formance of those functions which administer to its full development and growth. There are 

 still other points to be determined, where the animal furnishes from its system products useful 

 and necessary in civilized life, as milk and wool : hence we wish to know what influence food 

 has upon those products ; how their quality and quantity is affected by the agencies to which 

 they are exposed. The effects of cold and heat, dryness and moisture, have each their influence 

 upon the animal system. Exercise and rest have also their share in modiyfying the products 

 of organization. To these it is necessary to add a kind disposition, and an aptitude to acquire 

 or be taught, along with which it is evident gentleness must have a place : so an attachment 

 to place, and a dislike to wander, are important points in all animals. In illustration of the 

 foregoing statements, let me inquire, who does not know that it is difficult to improve the 

 condition of restless animals, or any animal, by giving it food which contains neither fat, oil, 

 amilaceous or saccharine matters ; or who would feed an animal upon these alone, who wished 

 to give muscle and bone their due proportions. It is but a truism to assert, that we can not 

 get from a body an element which is not in it. Inorganic matter can not be obtained from any 

 of the numerous compounds of carbon, hydrogen, oxygen and nitrogen. The constant de- 

 mand for food is an important fact to be considered in the economy of animals ; this is true 

 when they cease to grow, and it is also true that they ingest a greater quantity than the sys- 

 tem appropriates. The constant want of aliments arises from molecular changes in all parts 

 of the system, by which a constant waste of tissues takes place, and from which it follows 

 that an opposite molecular change must also take place, to carry new molecules to the places 

 occupied by the effete and worn out ones, which are destined to be cast out of the system. 

 But waste does not go on uniformly in the tissues ; it is greatly modified by external and in- 

 ternal causes ; it differs in different animals ; it is rapid in proportion to the temperature and 

 rapidity of the circulation. In birds, muscular waste is rapid ; in carnivora, it is less rapid ; 

 but in reptiles it is slow, and by this we account for the long periods during which they can 

 fast, and also for the ability of some of the mammalia to pass a winter without food, or tempo- 



