THE PHYSIOLOGY OF EXERCISE. 325 



The idea of exercise as we have regarded it passes so gradually 

 over to hardening against frequently repeated injuries, that I am 

 tempted to place here also the adaptation of the organism to accustom 

 itself to endure poisons. Without going back as far as King Mithri- 

 dates, many men have by habit made themselves comparatively proof 

 against alcohol, nicotine, and the alkaloids of opium. The North-Ger- 

 mans are only too proof against Pettenkofer's man-poison (my an- 

 thropotoxine) in badly ventilated assembly-halls, railway-carriages, 

 etc., to which fire-place people, like the English, are so sensitive. This 

 inurement can hardly be called self -improvement. 



You have, perhaps, gentlemen, been waiting in impatient expect- 

 ancy for me to speak on the subject you first thought of when you 

 heard that my address was to be on exercise. By exercise we under- 

 stand commonly the frequent repetition of a more or less complicated 

 action of the body with the co-operation of the mind, or of an action 

 of the mind alone, for the purpose of being able to perform it better. 

 Not without a purpose have I deferred the consideration of this kind 

 of exercise to this point, for it is quite different from the kinds pre- 

 viously spoken of, although those kinds may be connected with it. 

 This fundamental difference has not as yet been duly considered. We 

 seek in vain in most physiological text-books for instruction respect- 

 ing exercise ; if it is given, only the so-called bodily exercises are 

 generally considered, and they are represented as merely exercises of 

 the muscular system ; therefore it is not strange that laymen in medi- 

 cine, professors of gymnastics, and school-teachers generally believe 

 that. Yet it is easy to show the error of this view, and demonstrate 

 that such bodily exercises as gymnastics, fencing, swimming, riding, 

 dancing, and skating are much more exercises of the central nervous 

 system, of the brain and spinal marrow. It is true that those move- 

 ments involve a certain degree of muscular power ; but we can con- 

 ceive of a man with muscles like those of the Farnesian Hercules, who 

 would yet be incompetent to stand or walk, to say nothing of his ex- 

 ecuting more complicated movements. For that we have only to add 

 to our conception the power of arranging the motions suitably, and of 

 causing them to work harmoniously. 



Thus it becomes clear, if proof were needed, that every action of our 

 body as a motive apparatus depends not less, but more, upon the proper 

 co-operation of the muscles than upon the force of their contraction. 

 In order to execute a composite motion, like a leap, the muscles must 

 begin to work in the proper order, and the energy of each one of them 

 (in Helmholtz's sense) must increase, halt, and diminish according to a 

 certain law, so that the result shall be the proper position of the limbs, 

 and the proper velocity of the center of gravity in the proper direc- 

 tion. We know little as yet of the way in which we impart a definite 

 duration to the energy of the muscles, for our researches have so far 

 informed us upon little else than the convulsions following extremely 



