NUTRITION. 
45 
CHAPTER VI. 
NUTRITION. 
Nutrition is the earliest and most constant of vital op¬ 
erations. So prominent is the nutritive apparatus, that 
an animal has been likened to a moving sac, organized to 
convert foreign matter into its own likeness, to which the 
complex organs of animal life are but auxiliaries. Thus, 
the bones and muscles are levers and cords to carry the 
body about, while the nervous system directs its motions, 
in quest of food. 
The objects of nutrition are growth, repair, and propa¬ 
gation. The first object of life is to grow, for no animal 
is born finished. Some animals, like plants, grow as long 
as they live ; 19 but the majority soon attain a fixed size. 
In all animals, however, without exception, food is wanted 
for another purpose than growth, namely, to repair the 
waste which is constantly going on. For every exercise 
of the muscles and nerves involves the death and decay 
of those tissues, as shown by the excretions. The amount 
of matter expelled from the body, and the amount of nour¬ 
ishment needed to make good the loss, increase with the 
activity of the animal. The supply must equal the de¬ 
mand, in order to maintain the life of the individual; and 
as an organism can make nothing, it must seek it from 
without. Not only the muscles and nerves are wasted by 
use, but every organ in the body; so that the whole struct¬ 
ure needs constant renewal. An animal begins to die the 
moment it begins to live. The function of nutrition, 
therefore, is constructive , while motion and sensation are 
destructive . 
