70 ON THE STUDY OF rHYSlOLOGY. 



jjcrty ill question accompanying each other. Thus we say 

 that gold is yellow, ductile, soluhle in nitro-muriatic acid, 

 because we have always found gold, when pure, to be so. 

 We assert that living muscular fibres are irritable, living 

 nervous fibres sensible, for the same reason. The evidence 

 of the two propositions presents itself to my mind as un- 

 marked by the faintest shade of difference. 



Having found by experience that every thing we see has 

 some cause of existence, we are induced to ascribe the 

 constant concomitance of a substance and its properties to 

 some necessary connexion between them : but, however 

 strong the feeling may be, which leads us to believe in some 

 more close bond, we can only trace, in this notion of neces- 

 sary connexion, the fact of certainty or universality of con- 

 currence. Nothing more than this can be meant, when a 

 necessary connexion is asserted between the properties of 



variety of circumstances, and consider, at the same time, all the changes that 

 are, or may be, in these circumstance?, its immediate eflects. When ne : peak 

 of all the qualities of a body, or all its properties, we mean nothing more, 

 and we mean nothing less. Certain substances are conceived by us, and certain 

 changes that take place in them, which, we believe, will be uniformly the 

 same, as often as the substances of which we speak exist in circumstances 

 that are exactly the same. 



" The powers, properties, or qualities of a substance, are not to be re- 

 garded, then, as any thing superadded to the substance, or distinct from it. 

 They are only the substance itself, considered in relation to various changes 

 that take place, when it exists in peculiar circumstances." 



We cannot be surprised, that the author of the Physiological Lectures 

 should have poured forth the full vials of his wrath on doctrines at once com- 

 pletely subverting all his airy structures of subtle fluids, mobile matters, &c. 

 &c. considered as causes of vital actions, and so simple and logical, that any 

 attempt at direct opposition by reasoning would be utterly hopeless. He 

 therefore boldly affirms, that " if they mean to insinuate that we have no 

 knowledge of cause or effect beyond that which results from mere observa- 

 tion, they publish at the same time a libel on the human understanding, a 

 prohibition to rational inquiry, and a most severe satire on themselves,'* 

 P. 91. Unless the author should shew, on some future occasion, what he has 

 not even attempted on the present, viz. what it is that the words cause and 

 effect denote, in addition to relative invariable antecedence and consequence, 

 this volley of hard words will only recoil on his own head. 



