314 THE AMERICAN NATURALIST. [VOL XXXIII. 
rangement that just those vital processes which demand the 
most time, continuing as they do throughout our whole life, 
need no assistance from our consciousness, but are performed 
automatically. 
It will now be my purpose to show how the preservation of 
the equilibrium may be accomplished, how we can stand and 
move without being conscious of the complicated mechanism 
brought into action, and yet without constantly falling. We 
shall also take occasion to mention derangements of this mechan- 
ism, for right here we shall find many indications which are 
important for the comprehension of normal conditions. 
We begin with the simplest process of standing erect: 
Sehe jeder, wie er’s treibe, 
Und wer steht, dass er nicht falle. 
What, then, happens when we remain quietly standing erect? 
In order to do this a great number of our muscles, indeed 
nearly all the muscles of the trunk and lower extremities, must 
coéperate. The impulse for this coöperation is transmitted to 
the muscles from the brain; but in order to stimulate the 
muscles properly, the brain needs a number of external im- 
pressions, sensations, which incite the impulse, and regulate it. 
We shall then have to inquire how the muscles must codper- 
ate to produce the erect position. We shall endeavor to pene- 
trate farther into the secret of the complicated apparatus of 
the brain, which works so nicely, and, finally, we shall turn 
our attention to those sensations which furnish the necessary 
material for this part of the activity of the brain. 
I have mentioned above how great a number of muscles is 
required simply for standing. It is not necessary, however, 
that all the muscles concerned should contract; if all our 
muscles were in a state of strong contraction, making the body 
stiff and motionless, we should be as unstable as a broomstick 
which had been placed upright on the floor. It is, rather, 
_ necessary that each of these muscles contract with a certain 
strength, up to a definite point, so that each little inclination 
of the body be counteracted by a stronger contraction of the 
opposing muscles, while others are correspondingly relaxed. 
