PHYSIOLOGY. 103 



corporeal organ is employed, all the operations of thought, aris- 

 ing in consequence of sensation, are operations of the brain, and 

 are modified by its various condition. (Boerh. Inst. Med. 581. 

 Haller, Prim. Lin. ^Q.-^Gaub. Path. Med. 523. See af- 

 terwards CXXII.) 



" A circumstance relative to physiology, to which I sus- 

 pect you are not very attentive, is the history of human opin- 

 ions, which is by many considered as of little importance. 

 The confuting of opinions manifestly false, and long ago ex- 

 ploded, may indeed be considered as a very trifling labour; 

 and, if I were to entertain you with the confutation of the chemi- 

 cal or Cartesian opinions entertained more than a century ago, 

 I would employ your time very improperly ; but even this is 

 not so useless as has been supposed ; for as we must take our 

 facts from many authors, we must be acquainted with the spe- 

 culative opinions which influenced them. But it is absolutely 

 necessary that opinions which still subsist in the schools of 

 physic particularly if they are more especially fundamen- 

 tal with regard to system, and common to a great many differ- 

 ent persons should be considered here, and that I should 

 enable you to judge of their truth or falsehood. I speak all 

 this with a view to the Stahlian system, which within these forty 

 years has occupied the minds of many physicians in Germany, 

 and has spread more or less into every country of Europe. A 

 very ingenious gentleman in this country, Dr. Porterfield, re- 

 ceived this doctrine; and in England, Dr. Nichols, who also 

 infected Dr. Mead his father-in-law, in his old age. It has 

 made a considerable figure in France, in the hands of Sau- 

 vage, as it did formerly in the hands of Perrault ; and I have 

 shewn how far it has influenced Dr. Gaubius. The influence 

 of this system every where tends to corrupt not only the theory, 

 but likewise the practice of physic ; and it has made us lose 

 many excellent hands and many facts which we should other- 

 wise have had. I own, that in making up this compendium of 

 physiology, I thought that it was necessary to introduce a very 

 full confutation ; but I know that the subject is embarrassed 

 by many metaphysical difficulties, and I now see that it occu- 

 pies a greater part than I wish it to do, so that I shall give a 

 shorter commentary upon it than usual. One step towards des- 



