PHYSIOLOGY. 7 



ly any sort of motion, connected with the exercise of the func- 

 tions, which is not performed by muscles, or muscular fibres, so 

 that they must be a very fundamental consideration in the ani- 

 mal economy. When we trace the matter further, a little an- 

 atomy must teach us that there is not a muscular fibre which 

 has not a connexion with nerves ; and this connexion with 

 nerves is necessary to the action of the muscular parts for 

 compressing or cutting through these nerves destroys the action 

 of the muscles which are connected with them ; and the mus- 

 cles must not only be connected with these nerves, but, through 

 them, with the brain ; for the nerve being cut through in any 

 part of its course, the action of the muscle is destroyed. And 

 when we consider what it is in the brain with which the mus- 

 cles are thus connected, we find that by much the greater part 

 of the muscles of the body do not stir unless there is a certain 

 operation of the mind that we call the will, which excites and 

 directs the action of almost every muscular part We may 

 trace the matter still farther : The will may be primary and 

 independent, but, at the same time, we can, for the most part, 

 very clearly perceive that the will arises in consequence of sense. 

 Unless I see you before me, or unless I at least imagine you 

 present before me, I will not open my mouth to speak. It is 

 the sight of some agreeable object that determines my will to 

 put forth my hand, and bring the object nearer ; and it is the 

 feeling of something disagreeable that must direct me to put the 

 object from me : so that, in most cases, the will depends upon 

 sense. In the next place, we may inquire what sense is, and 

 how it arises ; and we can perceive that it depends upon the 

 extremities of certain nerves expanded upon particular parts 

 of the body, and fitted to receive the impulses of external bodies, 

 which, acting upon these extremities, give what we call sensa- 

 tion ; and this, at last, produces will. Further, there is an im- 

 pulse upon certain extremities ; but these again are connected 

 with a course of nerves which ultimately end in the brain ; for, 

 if the nerve between the brain and organ of sense be cut through, 

 or otherwise destroyed, all sense ceases. In the fundamental 

 operations of the human body, therefore, the nerves, and the 

 parts connected with them, are especially concerned ; and as 



