THE INFLUENCE OF EXERCISE UPON HEALTH. 331 



To realize more definitely the work which the skin does, consider 

 the fact that a square inch of skin is calculated to contain twenty- 

 eight thousand pores. These pores, if healthy, are at all times puri- 

 fying the blood by insensible perspiration, and in times of vigorous 

 exercise make that perspiration very sensible. This sensible perspira- 

 tion is essential to health, for the pores must occasionally be opened 

 wide and flushed, in order to cleanse them thoroughly. Not only is 

 this action of the skin in exercise increased by the increased flow of 

 blood to the surface, but also by the mere motion of the muscles under 

 the skin. This last effect might be called the direct effect of exercise 

 on the skin. How close this connection is between the skin and mus- 

 cles may be seen from the fact that " any part of the skin of the hand 

 is in connection with, perhaps, two hundred muscles." This " fact, 

 showing the exceedingly numerous and complicated communications 

 between a given portion of the skin and the moving organs," * makes 

 it easy to conceive how the skin is stimulated to action directly by 

 exercise. 



Bodily exercise is essential to the healthy action of the brain and 

 the nerves. There is no real conflict between brain-work and body- 

 work. Brain presupposes body ; can not exist without it ; is depend- 

 ent upon it for support and nourishment. Brain can not communicate 

 with the external world, nor with other brains, so far as we know, ex- 

 cept through the medium of the body. Consider how brain-power is 

 formed and grows in a child. Is not the first exertion of mental 

 power, as well as the first sign of life, connected with motion ? Back 

 of the child's outstretched hand there is in the mind a desire for some- 

 thing and a will to obtain it. Each consciously directed muscular 

 action has two effects, one on the muscle used, another on the direct- 

 ing brain. Can there be any doubt that this mutual action of brain 

 and body contributes to the growth of each ? Can there be any fur- 

 ther doubt that, the more organs which the brain supervises, and the 

 more muscles which it controls and directs, the more opportunity the 

 brain has for growth ? " Brain is evolved from the organization." f 

 First, there is " growth, the force for which was supplied from a hun- 

 dred sources " ; and, secondly, there is " a power grown. . . . No per- 

 fect brain ever crowns an imperfectly developed body." This, then, up 

 to a certain time of life, is Nature's method of forming brain-power, 

 viz., by the conscious activity of the bodily powers. The fact that 

 most people are right-sided as well as right-handed is registered in 

 their brains ; the left side of the brain, which supervises the right side 

 of the body, being generally the larger. 



In this growth of the brain, the whole nervous system is involved. 



The spinal cord (almost a continuation of the brain), and every nerve, 



which from each organ brings intelligence of want, and every nerve 



that flashes the order to supply that want, all are brought into action 



* Bain. \ " Building of a Brain," Dr, Edward H. Clarke. 



