116 HUMAN PHYSIOLOGY 



this function. This will be a good time to outline the 

 reflex adjustments by which the balance is preserved. 



A statue of a man is a most unstable object. It 

 cannot be relied on to keep its feet when there are forces 

 tending to upset it. But we see the living body main- 

 taining an erect position in the midst of disturbing 

 circumstances, bracing against the wind, adapting itself 

 to slopes, and saving itself from falling again and again. 

 The mind is ordinarily but little occupied with these 

 processes; they seem to take care of themselves. To say 

 this, is practically to say that the reflex principle is 

 involved. We shall find that this is clearly the case. 



The body is always swaying more or less. Each 

 oscillation threatens a fall, but normally there is a timely 

 check and reversal of the movement. If this is a re- 

 flex we must seek to show what receptors are stimulated 

 to insure the reaction. We have to recognize several 

 orders. The following are certainly to be included: 

 (1) those in the soles of the feet, (2) a great number in 

 the muscles, tendons, and joints, (3) the eyes, and (4) 

 the internal ears. The order does not necessarily 

 indicate their relative importance. 



1. When one sways forward the pressure on the soles 

 of the feet becomes lessened at the heels and increased 

 at the toes. If the body tilts to the right the pressure 

 upon that foot is increased and the weight borne by 

 the left foot is diminished. There are receptors in the 

 soles which are responsive to stimulation by pressure. 

 The afferent currents which result have a long course 

 to run to reach the brain. In the gray matter of the 

 cerebellum, and probably in other places too, they 

 generate efferent impulses which play upon the motor 

 cells of the cord and secure purposeful contractions of 

 various muscles tending to restore the balance. 



2. Any swaying of the body alters the tension of 

 many muscles and their associated connective tissues. 

 The bearing upon one another of the small bones in 

 the feet is subjected to change, the stresses in all the 



