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 mechanical 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 example 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 better fitted for that office. After what has been said above, we can with some justification add to this question the many times more