326 THE POPULAR SCIENCE MONTHLY. 



brief excitations, and upon tetanus. Since the nerves only trans- 

 mit the impulses coming from the motor-ganglion cells, it is evident 

 that the peculiar mechanism of the composite movements resides in 

 the central nerve-system, and that, consequently, exercise in such move- 

 ments is really nothing else than exercise of the central nerve-system. 

 This possesses the invaluable property that the series of movements 

 (if we may speak thus), which take place in it frequently after a 

 definite law, are readily repeated in the same order, with the same 

 swell and ebb and intricacy, whenever a singly felt impulse of the will 

 demands it. Thus, all the bodily exercises we have mentioned above 

 are not mere muscle-gymnastics, but also, and that pre-eminently, 

 nerve-gymnastics, if for brevity we may apply the term nerves to the 

 whole nervous system. Johann Miiller, whose explanations, in the 

 second volume of his " Hand-book of Physiology," still appear to me 

 the best that have been written on the theory of movement, has recog- 

 nized this double nature of bodily exercises, but has not sufficiently in- 

 sisted upon it. On this, he makes a remark which strikingly enforces 

 our view; that is, that improvement in exercises of the body often con- 

 sists nearly as much in the suppression of unessential by-motions as in 

 acquiring dexterity in necessary motions. Observe the active boy who 

 for the first time raises himself upon a ladder with his hands. Al- 

 though it is of no use to him, his arms and his legs shake at every 

 grasp. After a few weeks he holds the hips, knee and foot joints of 

 his closely locked legs tautly extended. The suppression of by-motions 

 furnishes unconsciously to us a mark of the pleasing appearance of the 

 well-drilled soldier, of the skilled gymnast, and of the cultivated man ; 

 chorea begins when they are let loose. We know nothing of the 

 mechanism of the suppression of by-motions, yet it is evident that, 

 when muscles remain at rest in the course of exercise, the result of the 

 exercise is not to strengthen them. 



Under continuous severe exertions, as in mountain-climbing and 

 long walks, the heart begins to beat faster and more strongly, and op- 

 pression of the breath is felt, because, according to Johann Miiller, 

 the heart participates in a by-motion ; in Traube's opinion, because 

 it is stimulated by the excess of carbonic acid formed in the laboring 

 muscles. How is it, then, that exercise diminishes these palpitations ? 

 Is it by means of the vagus nerve ? 



Perspiration under exertion may also be regarded as a by-secre- 

 tion as well as the greater secretion of saliva in speaking and chewing ; 

 and the diminished perspiration of our blacksmith when taught would 

 then be the suppression of this by-secretion, which might be compared 

 to a by-movement, through exercise. The beating of the -heart and 

 perspiration are, however, involuntary, and it is very questionable 

 whether we can refer the stopping of them by means of exercise to 

 such processes. 



Still, something else than the control of the muscles by the motor- 



