d. The plant lives on
fluid nutriment, and this comes to it by the process of diffusion in
every drop of water and breath of air. The acquisition of food
requires no effort, and the plant makes none. It has therefore
always remained stationary and almost insensible. Not taking the
first step it has never taken any of the higher ones. But solid food
would not, as a rule, come to the animal--though stationary and
sessile animals are not uncommon in the water--he must go in search
of it. This called into play the powers of locomotion and
perception. And in the sequence of function we have seen digestion
calling for the development of muscle; and muscle, of nerve and
brain. And the brain became the organ of mind.

Man as a mere animal is necessarily active and energetic; otherwise
he stagnates and degenerates. Labor is a curse, but work a blessing;
and man's best work, of every kind, is done in the friction of life,
not in ease and quiet. Man is, further, a being composed of cells,
tissues, and organs, which were successively developed for him by
the lower animal kingdoms. The old view, that man was the microcosm,
had in it a certain amount of every important truth. We need to be
continually reminded of our indebtedness in a thousand ways to the
lowest and most insignificant forms of life.

Man is a vertebrate animal. This means that he has a locomotive, not
protective, skeleton, composed of cartilage--a tough, elastic,
organic material, hardened, as a rule, by the deposition of mineral
salts, mainly phosphate of lime, in exceedingly fine particles, so
as to form a homogeneous, flawless, elastic, tough, light, and
unyielding skeleton, held together by firm ligaments.

The skeleton is internal, and this fact, as we have seen, gives the
possibility of large size. And size is in itself no unimportant
factor. Professor Lotze maintains that without man's size and
strength, agriculture and the working of metals, and thus all
civilization, would have been impossible. But we have already seen
that there is an extreme of size, _e.g._, in the elephant, which
makes its possessor clumsy, able to exist only where there are large
amounts of food in limited areas, slow to reproduce, and lacking in
adaptability. This extreme also is avoided in man; in this, as in
many other particulars, he holds the golden mean. But we have also
seen that large size is, as a rule, correlated with long life and
great opportunity for experience and obser