S l . RUCTURE OF SENSIFEROUS ORGANS 305 



in the nerve or in the sensorium, by the operation 

 of a cause distinct from the affection of the sense 

 organ by an odorous body. Such " subjective " 

 sensations are as real existences as any others, and 

 as distinctly suggest an external odorous object as 

 their cause; but the belief thus generated is a 

 delusion. And, if beliefs are properly termed 

 " testimonies of consciousness," then undoubtedly 

 the testimony of consciousness may be, and often 

 is, untrustworthy. 



Another very important consideration arises 

 out of the facts as they are now known. That 

 which, in the absence of a knowledge of the phy- 

 siology of sensation, we call the cause of the 

 smell, and term the odorous object, is only such, 

 mediately, by reason of its emitting particles 

 which give rise to a mode of motion in the sense 

 organ. The sense organ, again, is only a mediate 

 cause by reason of its producing a molecular 

 change in the nerve fibre; while this last change 

 is also only a mediate cause of sensation, depend- 

 ing, as it does, upon the change which it excites 

 in the sensorium. 



The sense organ, the nerve, and the sensorium, 

 taken together, constitute the sensiferous appara- 

 tus. They make up the thickness of the wall 

 between the mind, as represented by the sensation 

 " muskiness," and the object, as represented by 

 the particle of musk in contact with the olfactory 

 epithelium. 



