324 THE POPULAR SCIENCE MONTHLY. 



The self -improvement of the series of connecting tissues by exer- 

 cise in other members, takes place in a more peculiar manner, rather 

 mechanical than chemical and physiological. The motions of the 

 joints are made easier by exercise ; and making stiff joints movable 

 is one of the most grateful objects of orthopedy. Herr Henke ex- 

 plains the unusual suppleness of the so-called India-rubber men as the 

 result of relaxation of the ligaments, a disappearance of edge-surfaces 

 of bone, and a diminished radius of curvature of the sliding surfaces, 

 but particularly of a prolongation of the flesh-fibers at the expense of 

 the tendons. Possibly an elastic tissue is formed in the ligaments of 

 their limbs. "Whether such a tissue grows in the vocal cords after ex- 

 ercise in vibrating them is still uncertain. 



To make our statement complete, the increased ease in labor 

 bought, it is true, at the cost of greater danger of secondary bleedings 

 of those who have borne many times, belongs here. We may also 

 regard as a self -improvement, although belonging to another region, 

 the relaxing after-birth, and the accompanying reflex action of the 

 breast upon the uterus. 



The glands are another class of tissues the efficiency of winch is 

 raised by exercise. The sexual glands the milk- glands and testicles 

 are known to be capable of remaining at rest for years and even 

 for life, while their tissues are subject to a considerable diminution, as 

 is also normally the case with animals during the intervals between 

 the periods of heat. Inversely the sexual glands attain a wonderful 

 degree of production by means of alternations of rest and activity, as 

 is exemplified by stallions, milch-cows, sheep, and goats. If the breast- 

 glands are not kept exercised by sucking, the udder by milking, they 

 dry up and sink to rest till they are newly excited in sympathetic 

 action with the uterus. The same can not be immediately proved of 

 the fluids of secretory glands, but it is hardly doubtful that a digestive 

 vessel that is kept active by two meals a day, with its glandular attach- 

 ments, will dispose of a larger quantity of the various digestive fluids 

 than that of a penitent. The kidneys of the practiced beer-drinker give 

 passage to an incredible quantity of fluid. Finally, one who reads in 

 the sketches of the manners of the last century of the continual weep- 

 ing of the sentimental men and women of the time, will hardly be 

 able to restrain the presumption that their tear-glands were brought 

 up to the work by practice. We are as ignorant concerning the mech- 

 anism of the self-improvement of the glands through exercise as con- 

 cerning the process of secretion in them. Since this process is different 

 in nearly every gland, according to what nerves are introduced in 

 one the secreted matter increases ; in another becomes fatty ; in an- 

 other persists unchanged, but receives and gives out matter, or under- 

 goes changes in itself the problem appears twice as intricate and the 

 information doubly scanty, so that at last we have to do again only 

 with an increased accession of matter and more frequent innervation. 



