20 PHYSIOLOGY. 



one of physicians also. Though they maintain the presence of 

 a soul and I think it necessary to the motions that occur in our 

 material part, yet they are far from considering that there is 

 any thing left to it as a rational soul, but that the mutual in- 

 fluence of the soul and body takes place by what may be called 

 a physical necessity ; that there is nothing arbitrary in the 

 power of the soul. And Dr. Whytt, after having occasion to 

 observe several instances of the influence of the mind upon the 

 body, says, < Nor can we consider the mind as acting either ig- 

 norantly or perversely, when it sometimes excites such motions 

 in the body as increase its own pain, and in the end prove more 

 hurtful than beneficial : for these motions do not proceed, as 

 the followers of Stahl have imagined, from any rational views 

 in the mind, or a consciousness that the welfare of the body de- 

 mands them, but are an immediate consequence of the disa- 

 greeable perception which excites it into action. 1 * (On Nervous 

 Disorders ; Works, p. 520.) s He is more explicit still in his 

 Treatise upon Vital Motions, where he considers the share 

 which the mind has in producing motions : * The mind in carry- 

 ing on the vital and other involuntary motions, does not act as 

 a rational, but as a sentient principle, which, without reasoning, 

 is as certainly determined by an ungrateful sensation or stimu- 

 lus affecting the organs, to exert its power in bringing about 

 these motions, as is a scale which, by mechanical laws, turns 

 with the greatest weight/ 1 (Works, p. 152.) This is esta- 

 blishing, in the strongest manner, a physical necessity in this 

 communication between the mind and body ; and I say, indeed, 

 that this has been the most common opinion among physicians. 

 I shall quote only two, but these, however, of the greatest au- 

 thority. Dr. Boerhaave speaks in this manner ; see his Insti- 

 tutions, 27. where he has these words, c Homo constat 

 mente et corpore unitis. Quorum utrumque natura ab altero 

 differt. Adeoque vitam, actiones, affectiones diversas habet ; n 

 but this is what you are to take notice of ' Tamen ita se 

 habent inter se, ut cogitationes mentis singulares determinatis 

 corporis conditionibus semper jungantur et vicissim. 1 * In short, 

 the soul and body are distinct substances; but they are so 

 united, that thought is constantly connected with certain states 

 of the body, and, on the contrary, that these states produce a 



