THE PHYSIOLOGY OF EXERCISE. 321 



of heat. Ludwig and Sadler showed on this point that, aside from 

 mechanical hindrances, the blood flows freer and richer through the 

 vessels of the working muscle. This is not only in the sense that new 

 combustible matter is introduced, but also in that the ashes are at 

 the same time swept away from the muscle-hearth ; since, according 

 to the discovery of Herr Johann Ranke, followed out by Hermann 

 Roeber, the acids formed by muscular activity depreciate the mechan- 

 ical and electrical capacity of the muscle, exhaust it chemically as we 

 are accustomed to say, without being able to conceive any other than 

 a chemical exhaustion of the muscle. Still less than of the chemical 

 mechanism of muscular contraction, have we a conception of what 

 takes place chemically in the strengthening of the muscle by exercise, 

 of how it becomes better fitted for work through a higher degree of 

 oxidation, and of why it falls away on the cessation of the changes 

 that take place in it in activity. It seems most natural to think 

 that these effects depend alone upon the increase and diminution 

 of the flow of blood during activity and during rest ; yet this of 

 itself only makes the case darker than if we had not ventured to 

 decide the question in such a way. Chemistry throws the manifold 

 varieties of muscle-flesh which our taste distinguishes with so much 

 refinement generally into one pot ; and the old statement, established 

 in knowledge, that English park-deer tastes flat, is still far from being 

 explained. 



A subjective explanation is finally to be mentioned. The tired 

 muscle, as long as it is becoming stronger through exercise, gives pain 

 for several days when it is used and when it is pressed upon. Even 

 a muscle which has been once or oftener hardened, or thoroughly 

 trained, gives pain when it is again put to work after a long idleness, 

 as we soon learn when we begin a journey on foot or on horseback. 

 Whoever, after a long interruption in gymnastic exercises, feels no 

 more pain, will make no further progress. The muscles hurt after 

 epileptic spasms. Even if we attempt to ascribe the feeling of the 

 muscles to the nerves of the tendons, joints, and skin, and the Vater- 

 Pacini bodies, we still should not imagine that they bring on the 

 pains in tetanus and trichinosis. Notwithstanding Sach's labors, we 

 are not yet in the light concerning the pathic nerves that bring about 

 these pains. Wherever and however they do it, they also produce 

 muscular aches after exertions. 



The improvement of the muscles by exercise, little as we know of 

 it, has* been established from antiquity, and, being relatively more 

 familiar, the best case of improvement, is fitted to serve as an ex- 

 ample for similar processes in other tissues. Indeed, the question 

 now is, whether other tissues than the cross-striped muscles are by 

 frequent exercise of their office in the animal household made bet- 

 ter fitted for that office. After what has been said above, we can 



x . . . 



with some justification add to this question the many times more 



vnr. ttt't 9,1 



