110 DR seller's memoir OF THE 



of a stimulus acting on an unconscious sentient principle. He does not say that 

 the animal is necessarily unconscious of the stimulus ; neither does he say that 

 the animal is unconscious of the muscular contraction which constitutes the 

 movement ; what he enforced is, that there is no consciousness of anything inter- 

 posed between the consciousness of the impression, and the consciousness of the 

 muscular contraction excited. For example, if a person sitting with his naked 

 foot on the fender, sees a tea-kettle about to boil over, he withdraws his leg ; if 

 on the other hand, some drops of boiling water fall on his foot without warning, 

 his leg is snatched back in spite of himself. In both cases there is the conscious- 

 ness of an impression preceding the withdrawal of the limb ; but between the 

 sight of the kettle about to boil over, and the consciousness of the muscular con- 

 traction by which the leg is moved backwards, there is the consciousness of a 

 voluntary act, the consciousness of the act of mind termed a volition. In the 

 second supposition, on the contrary, between the consciousness of the sensation 

 caused by the hot drops of water, and the consciousness of the muscular contrac- 

 tions concerned in moving back the leg, there is nothing directly discovered to 

 intervene. Here Whytt, not having learned to lay aside the philosophy of causes, 

 and to content himself with the expression of a law, infers that the movement is 

 caused by an unconscious act of a sentient principle. Had Whytt in such a case 

 omitted to assign a cause, he would not have satisfied those to whom he addressed 

 himself. Men were not then accustomed to be put off with a law of succession 

 between two phenomena in lieu of a cause. Doubtless they were then too often 

 treated to a supposition instead of a reality, when the}'^ asked for a cause ; yet 

 not oftener than in the present day a law is made to pass for an explanation, 

 when it is destitute of any such significance, being an individual case in a species 

 of facts, instead of being an example of a species known to belong to a genus of 

 facts. Reflex action, in all its vast extent, is but a species, which not being 

 yet referrible to a genus, receives no explanation, — it is a fact that may be multi- 

 plied to the utmost extent, without exhibiting anything of a generic character. 

 Gravitation itself would form but a species of facts, did it not include the heavens, 

 as well as the earth. 



To resume, Whytt moreover explains, that he could not dispense with this 

 sentient principle, because he saw no other mode of connecting the impression 

 from without with the more or less distant sources (that is, the origins of the 

 efferent nervous filaments) of the influence from within, by which a complex out- 

 ward movement was to be effected. Had the idea been developed in his day, of 

 the white fibres of the nervous system being merely internuncial, then there 

 would have been no need of such a principle. 



He represents, it is true, this principle as a part of the soul ; but doubtless he 

 would have been content had he believed in the purely internuncial office of the 

 white fibres to reduce it at least to its modern rank of a vis nervosa, which indeed 



