156 DISEASES OF SONES. 



our knowledge is incomplete if we do not go still 

 further, and see that blood is the stimulant which 

 causes its contractile power to act. And in like 

 manner with the eye, whose relations to light are 

 as essential a part of its constitution as the trans- 



Karency of its membranes or the convexity of its 

 3ns. Now in the case of the bones we are apt to 

 describe their hardness, their mobility, and other 

 qualities* without sufficiently adverting to the fact 

 that, being organs of resistance and motion, the 

 frequent and regular performance of motion and re- 

 sistance is as essential to their well-being as blood 

 is to the heart, air to the lungs, or light to the eyes. 

 And, accordingly, when that condition is not fulfilled, 

 the bones become feeble, diseased, and unfit for 

 their functions, just as the softer parts of the body 

 do. In practice* it is of the utmost importance to 

 be fully aware of this fact. 



It is familiar to the professional mind, that a part 

 deprived of that exercise or action which nature 

 destined it to fulfil becomes weakened, diminishes in 

 size, and at last shrivels and alters so much in appear- 

 ance as not to be recognisable. Thus, if an artery 

 the large artery which supplies the arm with blood, for 

 example be tied, and the flow of blood obstructed* 

 a change of structure immediately begins, and goes 

 on progressively, till, at the end of a few weeks, 

 what was formerly a hollow elastic tube presents 

 the appearance of a ligamentous inelastic cord. A 

 muscle condemned to inaction loses half its bulk in a 

 comparatively short time ; and if long unexercised* 

 at last loses entirely its power of contraction and 

 muscular appearance. The same rule holds with 

 all other parts of the system, and* in an especial 

 manner, even with the hard and apparently unalter- 

 able fabric of the bones. It is ascertained by ex- 

 tensive experience, that complete inaction, besides 

 diminishing the size, injures the structure of bone 

 so much as to deprive it of its hardness, and 



