PERCEPTION. 359 



they are, in their nature, as perfectly distinct as the subjects 

 in which they occur; that is, as mi?id is distinct from mat- 

 ter; and they cannot, therefore, be conceived by us as 

 having the slightest resemblance the one to the other. Yet 

 sensations invariably suggest to the mind ideas, not only of 

 the existence of an external agent as producing them, but 

 also of various qualities and attributes belonging to these 

 agents; and the belief, or rather the irresistible conviction, 

 thus forced upon us, of the reality of these external agents, 

 which we conceive as constituting the material world, is 

 termed P accept ion. 



Various questions here present themselves concerning the 

 origin, the formation, and the laws of our perceptions. This 

 vast field of curious but difficult inquiry, situated on the 

 confines of the two great departments of human knowledge, 

 (of which the one relates to the phenomena of matter, and 

 the other to those of mind,) requires for its successful culti- 

 vation the combined effi^rts of the physiologist and the me- 

 taphysician. For although our sensations are purely men- 

 tal affections, yet inasmuch as they are immediately depend- 

 ent on physical causes, they are regulated by the physical 

 laws of the living frame; whereas the perceptions derived 

 from these sensations, being the results of intellectual pro- 

 cesses, are amenable rather to the laws which regulate men- 

 tal than physical phenomena. It is certain, from innume- 

 rable facts, that in the present state of our existence, the 

 operations of the mind are. conducted by the instrumentality 

 of our bodily organs; and that unless the brain be in a 

 healthy condition, these operations become disordered, or 

 altogether cease. As the eye and the ear are the instruments 

 by which we see and hear, so the brain is the material in- 

 strument by which we retrace and combine ideas, and by 

 which we remember, we reason, we invent. Sudden pres- 

 sure on this organ, as in a stroke of apoplexy, puts a total 

 stop to all these operations of the mind. If the pressure be 

 of a nature to admit of remedy, and has not injured the tex- 

 ture of the brain, recovery may take place; and immediately 



