302 ON SENSATION AND THE UNITY OF 



the olfactory membrane offers, that we must seek 

 for the seat of the organ of the olfactory sense. 

 The only essential part of that organ consists of a 

 multitude of minute rod-like bodies, set perpen- 

 dicularly to the surface of the membrane, and 

 forming a part of the cellular coat, or epithelium, 

 which covers the olfactory membrane, as the 

 epidermis covers the skin. In the case of the 

 olfactory sense, there can be no doubt that 

 the Democritic hypothesis, at any rate for such 

 odorous substances as musk, has a good founda- 

 tion. Infinitesimal particles of musk fly off from 

 the surface of the odorous body; these, becoming 

 diffused through the air, are carried into the nasal 

 passages, and thence into the olfactory chambers, 

 where they come into contact with the filamen- 

 tous extremities of the delicate olfactory epi- 

 thelium. 



But this is not all. The " mind " is not, so to 

 speak, upon the other side of the epithelium. On 

 the contrary, the inner ends of the olfactory cells 

 are connected with nerve fibres, and these nerve 

 fibres, passing into the cavity of the skull, at 

 length end in a part of the brain, the olfactory 

 sensorium. It is certain that the integrity of 

 each, and the physical inter-connection of all these 

 three structures, the epithelium of the sensory 

 organ, the nerve fibres, and the sensorium, are 

 essential conditions of ordinary sensation. That 

 is to say, the air in the olfactory chambers may be 



