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- 
