Page:Popular Science Monthly Volume 11.djvu/613

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predictions in order that the public may be informed as to the probabilities of change.

It may be said that in the last two or three cases the purpose is intelligently appreciated, and that they are thus separated by a sharp line from the others; but this distinction gradually shades off and disappears as an action becomes habitual, and as soon as the habit becomes hereditary it may be entirely wanting.

The well-drilled soldier goes through with his evolutions without a thought as to his reasons for doing so, and nearly every middle-aged business-man of methodical habits probably recollects finding himself at his place of business on a holiday without knowing how or why he came there. One characteristic of these various actions is, then, that each has a purpose. Another is that, although the object of the action is the accomplishment of a purpose, the cause of the action is a change, external to the organism and distinct from the purpose.

The leaf of the Venus's-flytrap closes, and the digestive organs of an animal do their work, not because food is needed, but because they are excited by the presence of a foreign body. The dog points because he scents a particular odor, not because he wishes to do his duty. The soldier assumes his position because he hears the word of command, etc. The actions which are the subject of our present lecture stand, then, in a double relationship. They are excited by certain external changes, and they have for their object the accomplishment of a purpose. Herbert Spencer has expressed this dual relationship in a simple formula. According to him, these and all other peculiarly vital actions consist in "the adjustment of internal relations to external relations." This is not very lucid when stated abstractly, but perhaps an example will help to make it clear. If I kick a stone, I may move it a greater or less distance, and set up some slight molecular change within it, and hurt my foot, perhaps. If I kick a dead dog, the result is the same; but, if the dog is alive, I shall find that all these results follow, and something more. The molecular change in the nerves of the dog gives rise to or excites a series of actions adapted to meet my attack and to prevent further injury. There is a relation, external to the dog, between the kick and a disposition to do him further violence; and there is an internal relation in the dog between the sensation caused by the blow and a desire to escape the violence which is to follow; and whether he crouches and supplicates, or puts his tail between his legs and runs, or returns my attack, he simply adjusts internal relations to external relations. There is a relation between a downward direction and the presence of water in the ground, and to this relation the roots of the plant respond.

There is a relation between the presence of a foreign body in the stomach and food to be digested; and accordingly, when the stomach is excited by the sensation of contact with a foreign body, it be-