SENSATION AND THE SENSIFEROUS OKGANS 301 



charged with particles of musk ; but, if either the 

 epithelium, or the nerve fibres, or the sensorium 

 is injured, or if they are physically disconnected 

 from one another, sensation will not arise. More- 

 over, the epithelium may be said to be receptive, 

 the nerve fibres transmissive, and the sensorium 

 sensifacient. For, in the act of smelling, the 

 particles of the odorous substance produce a mole- 

 cular change (which Hartley was in all probability 

 right in terming a vibration) in the epithelium, 

 and this change being transmitted to the nerve 

 fibres, passes along them with a measurable 

 velocity, and, finally reaching the sensorium, is 

 immediately followed by the sensation. 



Thus, modern investigation supplies a repre- 

 sentative of the Epicurean " simulacra " in the vola- 

 tile particles of the musk ; but it also gives us the 

 stamp of the particles on the olfactory epithelium, 

 without any transmission of matter, as the equiva- 

 lent of the Aristotelian "form"; while, finally, 

 the modes of motion of the molecules of the ol- 

 factory cells, of the nerve, and of the cerebral 

 sensorium, which are Hartley's vibrations, may 

 stand very well for a double of the " intentional 

 species " of the Schoolmen. And this last remark 

 is not intended merely to suggest a fanciful 

 parallel ; for, if the cause of the sensation is, as 

 analogy suggests, to be sought in the mode of 

 motion of the object of sense, then it is quite 

 possible that the particular mode of motion of the 



