CONDITIONS OF MUSCULAR ACTION. 95 



cases of shipwreck for example, men previously 

 Wt;ll fed are wasted away by bodily labour when 

 deprived of a full allowance of food, and it will not 

 be difficult to form some conception of the import- 

 ance of this condition to the well-being of the mus- 

 cular system. 



Something more than mere muscle, however, is 

 required for the production of regulated or volun- 

 tary motion. The muscle itself, though perfect in 

 strength and in structure, would otherwise remain 

 inert. A stimulus is required to put it into activity, 

 and to direct its contraction ; and this stimulus is 

 conveyed to it by the nerves. As we write, the 

 muscles which move the fingers and guide the per 

 obviously follow the commands of the will ; and th 

 moment the will is withdrawn they cease to oper- 

 ate. If the will be feeble and undecided, the mus- 

 cular movements will be equally weak and irreso- 

 lute ; whereas, if the mind be powerfully excited 

 and the will energetic, strength, rapidity, and deci- 

 sion will equally characterize all the "movements 

 of the body. Under the intense excitement and 

 headlong fury of madness, the muscular action of an 

 otherwise feeble man acquires a force often ex- 

 ceeding all our powers of control. 



It will be at once perceived from this description, 

 that, in effecting voluntary motion, we must have 

 in operation, first, The brain, or organ of mind, as 

 the source of the will ; secondly, The nerves, which 

 convey the intimations of the will to the muscles ; 

 and, thirdly, The muscles themselves, by whose 

 contractile powers motion is produced. It will be 

 understood, also, why the number and size of the 

 nerves distributed to a muscle are in proportion, not 

 simply to its volume, but to the variety, frequency, 

 and vivacity of the movements required from it ; 

 and why some small muscles employed in many 

 combinations are therefore supplied with a greater 



