72 Ic 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



" The objection against the mind's produ- 

 cing the vital motions, drawn from their being 

 involuntary, must appear extremely weak ; 

 since there are a variety of motions equally 

 independent upon our will, which yet are cer- 

 tainly owing to the mind. Thus, as had been 

 already observed, the contraction of the pupil 

 from light, and the motions of the body from 

 tickling, or the apprehension of it, undoubt- 

 edly flow from the mind, notwithstanding their 

 being involuntary. The shutting of the eye- 

 lids, when a blow is aimed at the eye, is an- 

 other instance of a motion performed by the 

 mind in spite of the will; for, as the threat- 

 ened blow does not, by any corporeal contact, 

 affect the orbicular muscle of the palpebras, its 

 contraction must necessarily be deduced from 

 the mind, moved to perform this action from 

 the apprehension of something ready to hurt 

 the eye : and if there are some who, by an 

 effort of the will, can restrain this motion of 

 their eyelids, yet this dees not proceed so 

 much from the mind's making no attempt, in 

 consequence of the apprehended danger, to 

 close the palpebrse, as from the superior eye- 

 lid's being kept up by a strong voluntary con- 

 traction of its levator muscle. We cannot, by 

 an effort of the will, either command or re- 

 strain the erection of the penis ; yet it is evi- 

 dently owing to the mind: for sudden fear, or 

 anything which fixes our attention strongly 

 and all at once, makes this member quickly 

 subside, though it were ever so fully erected. 

 The titillation, therefore, of the vesicultE semi- 

 nnles by the semen, lascivious thoughts, and 

 other causes, only produce the erection of the 

 penis, as they necessarily excite the mind to 

 determine the blood in greater quantity into its 

 cells." 



Whytt's view is best explained in the follow- 

 ing passage of the same work : " Upon the 

 whole, there seems to be in man one sentient 

 and intelligent PRINCIPLE, which is equally 

 the source of life, sense, and motion, as of 

 reason ; and which, from the law of its union 

 with the body, exerts more or less of its power 

 and influence as the different circumstances of 

 the several organs actuated by it may require. 

 That this principle operates upon the body, by 

 the intervention of something in the brain or 

 nerves, is, I think, likewise probable; though, 

 as to its particular nature, I presume not to 

 allow myself in any uncertain conjectures ; 

 but, perhaps, by means of this connecting me- 

 dium, the various impressions, made on the 

 several parts of the body, either by internal or 

 external causes, are transmitted to and perceived 

 by the mind ; in consequence of which it may 

 determine the nervous influence variously into 

 different organs, and so become the cause of 

 all the vital and involuntary motions as well as 

 of the animal and voluntary. It seems to act 

 necessarily and as a sentient principle only, 

 when its power is excited in causing the 

 former; but in producing the latter it acts 

 freely, and both as a sentient and rational 



agent."* 



Op. cit., 8vo cd., p. TJ'). 



The third fasciculus of the Annotationes 

 Academicse of Geo. Prochaska was pub- 

 lished in 1784. It contains the Essay on 

 the Functions of the Nervous System. It is 

 impossible to speak too highly of this profound 

 and accurate dissertation. Although short, it 

 comprehends all the leading facts connected 

 with the working of the nervous system, and 

 affords abundant indications that its author had 

 thought deeply on the subject. I know of no 

 essay, of more modern date, which exhibits the 

 same profound knowledge of nervous pheno- 

 mena, and which is equally comprehensive. 

 How it came to be so long neglected can only 

 be explained by the too general incompetency 

 of physiologists to appreciate his views. Yet 

 his language is remarkably clear and precise. 

 No one can have done more ample justice to 

 his predecessors and contemporaries. His lite- 

 rary research was extensive and accurate, and 

 his historical summary is most interesting and 

 instructive. The attentive perusal of this essay 

 more frequently than once has impressed me 

 strongly with the conviction that Prochaska was a 

 man of the highest mental capacity and of great 

 power of generalization, and I shall rejoice to 

 see his work made easily accessible to all medical 

 readers. 



A brief summary of this important work will 

 not be out of place here. 



In the first chapter, the first seven sec- 

 tions are occupied with an historical account 

 of the views of preceding philosophers, begin- 

 ning with Aristotle and Galen. In the eighth 

 section, he remarks, " At length we abandon 

 the Cartesian method of philosophizing in this 

 part of animal physics, and embrace the New- 

 tonian, being persuaded that the slow, nay, the 

 most uncertain road to truth is that by hypo- 

 thesis and conjecture, but that by far the more 

 certain, more excellent, and the shorter way is 

 that, quse a posteriori ad causam ducit. Newton 

 distinguished the inscrutable cause of the phy- 

 sical attractions by the name ' force of attrac- 

 tion ;' he observed its effects, arranged them, 

 and detected the laws of motion, and thus esta- 

 blished a useful doctrine, honourable to human 

 genius. In this way we ought to proceed in the 

 study of the nervous system ; the cause latent 

 in the nervous pulp, which produces certain 

 effects, and which hitherto has not been deter- 

 mined, we shall call vis nervosa ; its observed 

 effects, which are the functions of the nervous 

 system, we shall arrange, and expose their laws, 

 and in this manner we shall be able to construct 

 a true and useful doctrine, qua; arti medicre 

 novam lucem et faciem elegantiorem datura est 

 pro certo.'' Haller, he admits, had previously 

 used the term " vis nervosa" to express the 

 power by which nerves cause muscles to con- 

 tract, but to Unzer he assisns the credit of 

 having thrown the greatest light upon this sub- 

 ject, although he states that to accommodate 

 himself to the times in which he wrote and to 

 make himself more generally understood, he 

 still used the term " animal spirits," although 

 his doctrine was quite independent of such an 

 hypothesis. 



In the second chapter Prochaska gives an 



