PHYSIOLOGY. 67 



renew its palpitations, and will not do the same when applied to 

 other muscles ; but that is not because the inherent power is 

 more moveable, but because being extremely weak, it will not 

 shew itself, if it has much to move. Now the muscles are at- 

 tached to bones and other parts, on which account they cannot 

 be raised so easily. But cut away a muscle from its attach- 

 ments in a recently killed animal, or in one yet living, and it is 

 as moveable, on the application of a pin, as the heart is. This 

 circumstance, therefore, may give the appearance of greater mo- 

 bility to the heart and some muscles. Again, mobility may be the 

 consequence of habit. It is, to me, a doubtful question if the 

 constitution of muscular fibres, taken singly, is so different as to 

 produce a different state of vigour in them, the force of mus- 

 cles is according to the number of their fibres ; and in no other 

 circumstance can the vigour be varied but by repeated exercise."" 

 XCII. The inherent power, or the contraction dependent 

 upon it, can be excited by certain applications made either to 

 the muscles themselves, or to the nerves connected with them ; 

 and, in either case, the effects of such application are so exactly 

 the same, as to allow us to conclude that the matter in the 

 nerves, and in the muscular fibres, is of the same kind. " A 

 very ingenious gentleman, Dr. Thomas Smith, a pupil of mine, 

 has written an inaugural dissertation, (De Actione Musculari, 

 Edin. \^&].) to demonstrate this very fact. He applied to 

 muscles and to nerves every variety of powers, mechanical or 

 chemical, which are supposed to act upon them. He employed 

 a great variety of different substances in this way ; and he could 

 alternately, or in circumstances well suited for comparison, ap- 

 ply them to both nerves and muscles. And what was curious, 

 he found that there are substances that we consider as stimulant, 

 which, when applied, appear manifestly sedative ; and that some 

 other substances suspected to be sedative, when thus applied, 

 are found to be stimulant, although that is a rare occurrence. 

 The general result is, that the same matter applied to the 

 muscle or nerve, constantly produces either contractions or 

 insensibility, and shows either stimulant or sedative powers, 

 and this equally, whether applied to the nerve or to the mus- 

 cle itself; and in no one instance did any diversity appear. 

 The experiments were nicely executed, and indeed they requir- 



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