THE SENSE OF SMELL. 283 



take, for instance, a simple smellable substance, like oil of roses, or a simple, 

 elementary one, as chlorine, we know precisely all its physical and chemical 

 qualities, but we arc unable to state which of these qualities makes it odorous, 

 why another gas, as, for instance, oxygen or hydrogen, is inodorous, that 

 is, does not act in the required way upon the nerve of smell, or rather, on the 

 Bubstance of its end organs. Our scientific ancestors, it is true, knew v/ell how 

 to got over this difficulty; they invented a fine name for the unknown principle 

 of odorous substances, and with that they were perfectly satisfied. They as- 

 sumed a special spiritus rector inherent in odorous substances, without, how- 

 ever, being able to connect any clear idea with that name. We must here again 

 decidedly come forth to combat an erroneous conception, though by so doing wo 

 risk being accused of useless repetition, having already in the general introduc- 

 tion commenced our warfare against the same deep-rooted error. Every one 

 uninitiated in science, when asked about the qualities which render a substance 

 smellable, will designate the odor itself as the quality inquired after, believing 

 that a certain odorous essence, from without, has come to our consciousness, aa« 

 a detached part of the essence of that substance which, by way of experience, 

 we have found out to be the neai'est cause of our sensation. Every one will 

 attribute the quality of the sensation to the external object which is the cause 

 of the sensation, as properly belonging to that object; this is the fundamental 

 error we speak of, the same which makes us attribute the blue or green color to 

 the external light, or to the light-spreading objects, to the "blue sky" or the 

 "green meadow," and the sound to the vibrating cord. We repeat: the quality 

 of the sensation of smell of which we become conscious has nothing in common 

 with any quality of a so-called odorous essence, just as little as light developed 

 by two carbon poles on the passage of a galvanic current has anything in 

 common with the properties of the two metals which have produced the galvanic 

 current, and have become the indirect causes of the carbon light, as essence 

 of violets is the indirect cause of the odor of violets. We need not repeat how 

 we are brought to attribute the qualities of all our sensations to the external 

 objects which the soul habitually imagines to be the cause of sensation; we 

 have seen how this way of rendering our sensations objective is, on the one hand, 

 the necessary result of the education of our senses in the service of the soul, 

 and, on the other, the principal condition of the measureless benefits they bestow 

 on it. It is, therefore, an error, the origin of which is unavoidable, and its ex- 

 istence indispensable; which science must recognize as error, but which it can- 

 not prohibit or destroy. The physiologist himself, who teaches yon that color 

 is not the quality of light, regards, like yourselves, the sky as blue, and the 

 trees as green, and as obstinately as yourselves places the sound in the cord, 

 and the scent in the violet; he fares like one seized by giddiness, who sees tables 

 and chairs whirling around him, and though convinced of their standing firmly 

 at their place is unable to resist the delusion. You all firmly believe in the 

 theory of the astronomers, that the sun is at rest and the earLh in motion, and 

 yet your eyes again and again give the lie to the great dogma enunciated by 

 Galileo. Fr^m sunrise to sunset they whisper to your soul of the sun what he 

 told of the earth; "and yet it moves," and your credulous spirit, which piously 

 follows the demonstrations of its first teachers, the senses, is easily seduced, 

 and, in spite of its better knowledge, accommodates all its conceptions to the 

 insinuations of the eyes. 



If we cannot explain what makes a substance smellable, what the sensation of 

 smell is, nor what series of physiological processes intervenes between the action 

 of an odorous substance on the cuticle of the nose and the rise of the sensation, 

 at least we are able to elucidate, in a popular way, some of the interesting con- 

 ditions within which a sensation of smell takes place. 



Everybody knows that odors are inhaled by the nose, that is, that a sensa- 

 tion of smell arises when odorous substances, blended with the atmospheric air, 



