CONDITIONS OF MUSCULAR ACTION. Q3 



the health of the whole body immediately influ- 

 enced. The mind itself is exhilarated or depressed 

 by the proper or improper use of muscular exercise ; 

 and it thus becomes a point of no slight importance 

 to establish general principles by which that exercise 

 may be regulated. 



The first requisite for healthy and vigorous mus- 

 cular action is the possession of strong and healthy 

 muscular fibres. In every part of the animal econ- 

 omy, the muscles are proportionate in size and 

 structure to the efforts required from them ; and it 

 is a law of nature, that whenever a muscle is called 

 into frequent use, its fibres increase in thickness 

 within certain limits, and become capable of acting 

 with greater force and readiness ; and that, on the 

 other hand, when a muscle is little used, its volume 

 and power decrease in a corresponding degree. 

 When in a state of activity, the quantity of blood 

 which muscles receive is considerably increased ; 

 and, in consequence, those which are much exer- 

 cised become of a deeper red colour than those 

 which are less used. The reason of this will be 

 evident, when we recollect that to every organ of 

 the body arterial blood is an indispensable stimulus, 

 and that its supply is, during health, always propor- 

 tioned to the extent and energy of the action. When 

 any part, therefore, is stinted of its usual quantity of 

 blood, it very soon becomes weakened, and at last 

 loses the power of action, although every other con- 

 dition required for its performance may remain un- 

 impaired. 



It is the infringement of this condition that entails 

 so much misery upon our young manufacturing popu- 

 lation, and even upon many of the inmates of our 

 boarding-schools. Wasted by excessive labour, 

 long confinement, and miserable diet, the muscular 

 system is stinted in growth, and weakened in struc- 

 ture ; and the blood, impoverished by insufficiency 

 of nourishing food and by a vitiated atmosphere, is 



