112 DR seller's memoir OF THE 



voluntary, involuntary, and mixed. He regards the purely involuntarj^ and 

 mixed sort, in reference to this principle, as falling under the one head of spon- 

 taneous movements. The purely involuntary movements to which he chiefly 

 refers are the vital movements before enumerated, such as the contractions of the 

 heart, those of the blood-vessels, and the like ; but as it is designed to speak of 

 these apart, all reference to them is for the present avoided. 



Many of the spontaneous movements which he cites as examples of his prin- 

 ciple are of the mixed kind, or at times under the control of the will. A few of 

 them, such as sneezing, cough, hiccup, and vomiting, may be pronounced abso- 

 lutely involuntary. Further, some of them contrast with others as being very 

 simple in their character, such as the closing of the pupil under a strong light, 

 the shutting of the eyelids when the eye is threatened, the adjustment of the 

 membranes of the internal ear by the small muscles within the tympanum to the 

 variations of sound. These obtain the name of simple, because, while the afferent 

 nervous filaments by which the outward impression is conveyed to the nervous 

 centre must all terminate in close proximity to each other, the efferent filaments 

 by which the motor-influence is transmitted to the muscular fibres concerned, can 

 hardly originate at any considerable distance from the former or from each other. 

 On the contrary, such spontaneous movements as respiration and its many modi- 

 fications, of which sneezing, cough, hiccup, are instances, full vomiting, degluti- 

 tion, the evacuation of the rectum, and of the bladder, while these movements 

 are still exempt from the control of the will, and a large class of cases resembling 

 voluntary acts in which the muscular effort is certainly involuntary, or at least 

 without intervening reflection, as in the case of hot water falling on the foot, are 

 all truly named complex acts ; because, though the afferent filaments conveying 

 the out^^'ard impression in these examples may spread over ]jut a small area of 

 the sensory organs, the efferent filaments carrying outwards the motor influence 

 being necessarily numerous, would seem to originate from points distant from 

 the former, and distant from each other in the central organs. 



The principle on which Whytt explains all such cases is, that the outward 

 impression (outward as respects the nervous centre) made on the peripheral 

 extremity of a nervous filament being conveyed to the brain, determines the 

 transmission of motor influence by another nervous filament reaching the mus- 

 cular fibres which are to be called into activity ; and that this effect takes place, 

 however distant the origin of the second filament, producing the motion, may seem 

 to be from the termination of the first filament, producing the necessary affection 

 of the nervous centre, that is, according to him, an unconscious operation of mind, 

 or of a sentient animal principle. 



The discovery of numerous before unnoticed relations between the several 

 parts of the nervous sj'^stem, much as it has improved the knowledge of the pur- 

 poses served by the peculiar conformation of the nervous organism, has not ma- 



