“Nach ehernen, eisernen, grossen Gesetzen,
Muessen wir alle unseres Daseins
Kreise vollenden.”

But man is an animal.  And the principal characteristic of an animal is that it eats a certain amount of solid food.  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 observation.  And these are the foundations of intelligence.  Hence the deliverance of the higher vertebrate, and especially of man, from any iron-bound subjection to instinct.