USE AND DISUSE OF ORGANS. 95 



of lime ill the soil. The same breed has been found to degen- 

 erate on the poorer sandy soils of Massachusetts unless allowed 

 a liberal artificial diet. The good effects, however, of soil, 

 climate and diet may be to a large extent obtained by careful 

 housing, local drainage, a warm southern exposure of build- 

 ings and parks, and a liberal system of artificial feeding. 



Ath. Excessive Use of Parts. — This, if it does not unduly ex- 

 haust the vitality of the part and its power of nutrition, will 

 certainly determine an increased development. This is indeed 

 a wise provision in the animal economy, to strengthen an organ 

 to perform the work demanded of it. We have a familiar in- 

 stance of its effects in the blacksmith's arm, or in the professional 

 dancer's leg. The extraordinary development of one kidney 

 when the other has been destroyed is equally characteristic. 

 A patch of inflamed skin (i. e. a pimple on the face) after- 

 wards grows long hair ; a cock's spur transplanted to his comb 

 grows to four or five inches long (Hunter). Hard work in- 

 creases the thickness of the scarf-skin on the hands, pads form 

 on the knees of the Ceylon sheep, which kneel to browse the 

 short herbage, and a new growth of bony matter is thrown out 

 on the concave aspect of a rickety and bent bone. These may 

 be all referred to the stimulus offered to nutrition in a more 

 abundant determination of blood and nervous energy to the 

 part, and the changes seen in the whole body in other cases are 

 equally the results of a more general stimulus to nutrition. 

 Thus, in the horse we have demanded the utmost exercise of 

 muscle, bone, brain and nerve, and have produced animals with 

 an extraordinary combination of these elements and of their 

 legitimate fruits, speed and endurance. In the Leicester sheep, 

 the Berkshire and Essex pigs, and the Shorthorn cattle, we have 

 fostered and stimulated fat, bulk and early maturity, till we 

 have all the energies of the system devoted to their production, 

 and in Ayrshires we have solicited the flow of milk till the 

 udder and accessory organs have drawn to themselves all the 

 available powers of the being. 



blh. Disuse &f Parts. — Conversely, parts thrown out of use, 

 waste, as witness the arm carried constantly in a sling, the mus- 

 cle on the outside of the shoulder joint sprained and disused in 

 so-called sv^eeney, and the wasting of paralyzed muscles 

 generally. Tame rabbits have the hind limbs shorter than wild 



