158 CONDITIONS OF HEALTH IN BONES. 



any more than the former. Wherever matter is the 

 subject, action implies waste of materials, and unless 

 this waste be made up by proportionate supplies, 

 exercise leads to speedy decay, such as we/see take 

 place where the exercise has been carried beyond 

 the limits of nature, and beyond what any supply 

 can compensate. Inaction, on the contrary, implies 

 almost stagnation, and is always attended by dimi- 

 nution of the vital functions ; as is exemplified, in 

 the extreme degree, in hybernating animals, which 

 pass months in sleep without food and almost with- 

 out breathing, and also in frogs found alive in 

 stones and trees, where they must have been dor- 

 mant for a great number of years. Inactive parts, 

 then, require little nutrition, because there is little 

 expenditure ; a"nd they require little force or energy, 

 because it would be not only useless but detrimental 

 to them. 



By a law of the constitution, manifestly arranged 

 with relation to this principle, when any part of the 

 system is active, it attracts to itself, by the simple 

 stimulus of that activity, an increased supply of 

 blood and nervous energy. The former enables it 

 to repair the waste of substance which action pro- 

 duces, and the latter gives an increased tone in har- 

 mony with the greater call made on its powers. If 

 the exercise is momentary and is not repeated, the 

 extraordinary flow of blood soon disappears, and 

 the nervous power falls to the usual standard : but 

 if it is continued for a time, and is recurred to at 

 regular intervals, a more active nutrition is estab- 

 lished ; a permanently greater supply of blood 

 enters the vessels, even during the intervals of in- 

 action ; and an increase of development takes place, 

 attended with increased facility and force of func- 

 tion. 



If, again, any part is not duly exercised, there is 

 no local stimulus to attract a large supply of blood 

 or abundant flow of the nervous fluid ; there is no 



