92 THE POPULAR SCIENCE MONTHLY, 



arched chambers certain delicate plates of bone project, and these, as 

 well as a considerable part of the partition between the two chambers, 

 are covered by a fine, soft, moist membrane. It is to this Schneiderian, 

 or olfactory, membrane that odorous bodies must obtain direct access if 

 they are to give rise to their appropriate sensations; and it is upon the 

 relatively large surface which 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 perpendicularly to the surface of the membrane, and form- 

 ing a part of the cellular coat, or epithelium, which covers the olfactory 

 membrane, as the epidermis covers the skin. In the case of the olfac- 

 tory sense, there can be no doubt that the Democritic hypothesis, at 

 any rate for such odorous substances as musk, has a good foundation. 

 Infinitesimal particles of musk fly off from the surface of the odorous 

 body, and, becoming diffused through the air, are carried into the nasal 

 passages, and thence into the olfactory chambers, where they come 

 into contact with the filamentous extremities of the delicate olfactory 

 epithelium. 



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-fibers, and these nerve-fibers, 

 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 interconnection of all these three structures, the epithe- 

 lium of the sensory organ, the nerve-fibers, and the sensorium, are 

 essential conditions of ordinary sensation. That is to say, the air in 

 the olfactory chambers may be charged with particles of musk ; but, if 

 either the epithelium, or the nerve-fibers, or the sensorium is injured, 

 or physically disconnected from one another, sensation will not arise. 

 Moreover, the epithelium may be said to be receptive, the nerve-fibers 

 transmissive, and the sensorium sensifacient. For, in the act of smell- 

 ing, the particles of the odorous substance produce a molecular change 

 (which Hartley was in all probability right in terming a vibration) in 

 the epithelium, and this change, being transmitted to the nerve-fibers, 

 passes along them with a measurable velocity, and- finally reaching the 

 sensorium, is immediately followed by the sensation. 



Thus, modern investigation supplies a representative of the Epicu- 

 rean simulacra in the volatile 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 equivalent of the Aristotelian "form"; 

 while, finally, the modes of motion of the molecules of the olfactory 

 cell, 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 sug- 

 gest 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, 



