322 THE POPULAR SCIENCE MONTHLY. 



easily answered one, whether other tissues diminish in consequence 

 of a failure to exercise them in their office. 



A physiological proof that the smooth muscles are strengthened by 

 exercise is wanting. The adaptation of the eye to near vision dimin- 

 ishes from childhood to age according to a regular law, notwithstand- 

 ing the constant exercise of the faculty ; but it does not follow from 

 this that Briicke's muscle does not gain strength, for its gain may be 

 more than compensated by the growing stiffness of the tissue and the 

 diminished elasticity of the crystalline lens. The fact that men see 

 imperfectly at close range what their occupation gives them little 

 occasion to regard, indicates that Briicke's muscle loses strength when 

 it is not used. The uterus has no occasion to be exercised, for it is 

 active only after long pauses, and gains a portion of new fibers every 

 time for that purpose. We know nothing of the movements of the 

 muscle-maw of the bird, which forms a transition to the cross-striped 

 muscles. On the other hand, such pathological facts as the hyper- 

 trophy of the muscles of the bladder and the pylorus under circum- 

 stances of extraordinary resistance leave no doubt that the smooth 

 muscles, like the cross-striped ones, are strengthened by labor. Thus 

 an empirical basis is given to Herr Rosenthal's supposition that the 

 immunity against cold conferred by cold-bathing depends upon the 

 exercise of the smooth muscles of the skin and their vessels, which 

 are intrusted with the lowering of the co-efficient of cooling of the 

 body in the cold. Cold washing and bathing are the gymnastics of 

 the smooth muscles. 



The young blacksmith, of whom we spoke a short time ago, had 

 gained another advantage from exercise besides greater strength in 

 the muscles of his arm : he ceased to burn his fingers. Every one 

 knows that the epidermis thickens on those parts of the skin that are 

 frequently subjected to pressure, rubbing, and the touching of hot 

 things and caustic fluids. Handling of tools, rowing, vaulting on the 

 rack and bars, produce a callus chiefly at the ends of the middle-hand 

 bones or in the palms ; glass-blowing produces callus on the inside of 

 the fingers. Recurrent blisters often result in callus. Under the 

 pressure of hard shoes the form of skin-thickening known as corns 

 takes the place of callus. Callus and corns have been histologically 

 investigated, yet we can not tell why the useful callus is formed here, 

 the painful corn there, to say nothing of our having a theory of the 

 processes. They fall in the category of what Herr Virchow calls for- 

 mative stimulation of the cell-complex, and regards, like the nutritive 

 stimulation, as the result of a general and fundamental property of the 

 elementary organisms. An increased supply of matter, immediately 

 conditioned on an increased flow of blood, also takes place here. Since 

 we can not well predicate a vis a fronts, enlargement of the vessels re- 

 mains the only yet possible step toward an understanding, and with 

 this we reach a closed gate before which many other problems are 



