488 VOLUNTARY MOTION. 



First as to the continuance of respiration during sleep. 

 If you irritate any part of a person asleep, an effort of some 

 kind is made to withdraw from the source of uneasiness, 

 and people turn in their sleep when uncomfortable ; fowls 

 perch on one leg, voluntarily contracting their claws be- 

 fore they go to sleep, and remain thus supported till they 

 awake, though the bent condition of the claw is much pre- 

 served by mere mechanism. But men will sleep standing : som- 

 nambulists unconsciously perform astonishing muscular move- 

 ments : and, while awake, we continue winking, coughing, 

 and often continue walking, or performing other voluntary ac- 

 tions, while our minds are totally absorbed in reflecting and give 

 no perceptible attention to our corporeal movements ; a person 

 will play even a rapid piece of music, familiar to him, while 

 thinking and perhaps talking of something else, and forgetting 

 that he is at the instrument, though originally each of the 

 infinite number of volitions requisite to the performance may have 

 been slow and laborious c : nay, a person may fall asleep after 

 beginning a very habitual set of actions, and continue them, 



c Dr. Whytt confounded mind and life, and, believing that they were an im- 

 material substance, and matter incapable of vital and mental properties or soul, 

 ascribed all the functions of animal bodies, human and brute, to a soul 

 diffused through every part. (Of the Vital and Involuntary Motions of Ani- 

 mals. 1751. sect. xi. obj. i.) But, notwithstanding this prejudice and hypothesis, 

 he shows that volition may be exerted without consciousness. " Many of the 

 voluntary motions are performed," he says, "when we are insensible of the 

 power of the will excited in their production. Thus, while in walking, we either 

 meditate by ourselves, or converse with others, we move the muscles of our legs 

 and thighs, without attending to it or knowing what we are doing. We are not 

 sensible of the eye-lids being kept open by the continued operation of the will 

 but yet, when drowsiness and sleep steal upon us, we find it requires a con- 

 siderable effort to prevent the falling down of the superior palpebrse. The same 

 thing is known of the muscles which support the head. The most probable 

 account of our ignorance of these things seems to be this ; namely, that we 

 not only acquire, through habit, a faculty of performing certain motions with 

 greater ease than at first, but also, in proportion as this facility is increased, we 

 become less sensible of any share or concern the mind has in them. Thus a 

 young player upon the harpsichord, or a dancer, is, at first, solicitous about 

 every motion of his fingers, or every step he makes, while the proficients or masters 

 in these arts, perform the very same motions, not only more dexterously, but 

 almost without any reflection or attention to what they are about. (Ib. obj. iii.) 



Mr. Dugald Stewart's chapter on attention (Elements of the Philosophy of 

 the Human Mind. 1792. ch. ii.) well deserves perusal, though published forty- 

 one years after Dr. Whytt's Essay. 



