PHYSIOLOGY. 19 



of occasional causes ; and Leibnitz has proposed a third, which 

 supposes the existence of a pre-established harmony. You may 

 consult these ; but I do not say a word of them, because when 

 I have considered them as well as I can, I cannot perceive 

 that they have the least effect or influence in explaining any 

 thing : they do not admit of any application, either in physic 

 or in any other part of science, that I see. With regard to 

 the mode of this mutual influence, it will be allowed that as 

 you adopt one or other of these hypotheses, it may affect religi- 

 ous belief, but it can have no effect in physic, so that it is 

 not my province to consider them. But I must say, that the 

 mutual influence being supposed and granted, physicians have 

 differed very much with respect to the degree and extent of 

 that influence, and therefore I am obliged to take some no- 

 tice of these opinions, though they truly have not such in- 

 fluence as has been imagined, nor is it necessary to adopt either 

 the one or other opinion upon the subject. There might be 

 certain philosophers who contradicted our general proposition, 

 and believed that there was no immaterial part of man nor any 

 soul, but supposed the whole phenomena, even those of thought, 

 to depend upon certain circumstances of matter and motion, 

 and, therefore, that the whole of the phenomena of the human 

 body, even those of thinking, are a matter of pure mechanism, 

 and arise from mechanical necessity. This is the system of the 

 materialists ; and there have some defenders of such a system 

 appeared lately ; but their sect is very narrow, and there are 

 few of such an opinion ; and, however those of our profession 

 may have been suspected of dangerous opinions, the physicians 

 have been generally sufficiently orthodox upon this point, and 

 they very universally admit the presence of a soul. My late 

 colleague, Dr. Whytt, has, I think, with great strength of ar- 

 gument, shown that the phenomena, even of the body itself, 

 cannot be explained but upon the supposition of a soul as a 

 sentient principle. It is to this writer that I proposed to refer 

 you ; as he considers the argument with a view to the ani- 

 mal economy and to physic, he is the proper authority to be 

 consulted for the demonstration of the immateriality of the soul 

 in the economy while in a living state. But I must explain 

 more particularly his opinion, and what has been the common 



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