THE SENSE OF SMELL. 279 



&c., have been elucidated witla wonderful acuteness, neitlier pliysics nor chem- 

 istry answers the questions, what agent excites the nerve of smell; by what 

 force musk or the ether of rose-leaves acts in this or that specific way upon the 

 organ of smell; why the oxygen of the air, a gaseous substance like the sti-ong- 

 scented musk vapor, is odorless. If, then, in spite of this testimonium i)auper- 

 tatis, we still endeavor to produce a popular esaay on this brancli of physiology, 

 we look for our justification in various reasons. Firstly, we hope to be able to 

 give our readers something of general interest in the little that has been made 

 out with positive exactness; secondly, we shall regard it as a merit if we can 

 enlighten our readers concerning what we do not know, and if we succeed in 

 dispelling some of the manifold deep-rooted erroneous ideas and conceptions 

 which still haunt the imaginations of those uninitiated in scientific research. 

 This negative part of our dissertation may even be the most meritorious part of 

 the task before us. 



Unfortunately, our very beginning must be with a negative truth, to which 

 we have already alluded in our introduction on the theory of the senses. We 

 do not know what a sensation of smell is, just as we are unable to explain and 

 describe the nature of a sensation of touch, sight, hearing, or taste. Those 

 conscious conditions of the soul, which we call sensations, defy all definition. 

 Let one try to describe the fragrance of a rose, or the scent of musk, or what 

 we call a spicy odor or a putrid smell, or to tell what distinguishes the scent of 

 a violet from the smell of putrescent meat. Indeed, this is a problem which 

 admits of no solution ; everybody knows how a violet smells, everybody pre- 

 serves in memory the often-felt nature of that sensation of smell, embodying it 

 in imagination, and recognizing it even when the sense of sight does not present 

 a violet as its apparent cause, but none is able to designate any characteristic 

 mark of that sensation, distinguishing it from the nature of other similar ones. 

 The designations which are used are therefore all borrowed from the external 

 causes ; they either directly name the object from which stxi odorous substance 

 is evolved, or which is itself odorouis in a gaseous form, (smell of roses, smell 

 of oil of roses,) or they are selected in accordance with qualities and conditions 

 under which external objects become smellable, (putrid scent, roast smell ) 

 When we enter a scented atmosphere, and, without knowing the object which 

 makes it so, desire to describe our sensation, we cannot do it without munition- 

 ing some object which on a previous occasion caused in us a sensation of smell 

 of the same quality, and therefore we say it smells like violets, like varnish, &c. 

 Sometimes we recollect only having experienced previously a similar odor, without 

 our memory having also preserved its cause, and in such cases we stand there 

 helpless, completely unable to designate to any one the character of the sensa- 

 tion of smell produced in us. That we are still less able to compare a sensation 

 of smell with a sensation of another sense — with a sensation of light or sound, for 

 instance — hardly needs an elucidation. Not even sensations of smell and taste, or 

 of smell and touch, which, as we shall soon see, the uninitiated are so prone to 

 mix up with each other, can in any way be compared with one another, how- 

 ever paradoxical this may sound. We speak, for instance, of the keen and pungent 

 smell of spirits of sal ammoniac, and yet the sensation thus designated as keen 

 and pungent is no sensation of smell at all, but a so-called common sensation — 

 a sensation of pain produced, not by an affection of the nerves of smell, but by 

 an irritation which the vapors of that substance cause in the fibres of the nerves 

 of touch spread through the cuticle of the nose — a sensation which has nothing 

 in common with the true sensation of smell simultaneously produced by the 

 same substance. We mistake it for a sensation of smell, because it simultaneously 

 arises with one of that sense, and because we find that, like the latter, it comes 

 from the nostril ; not every one knows that the sensation of smell is produced 

 in the upper parts of the cuticle of the nose, and the sensation of touch in the 

 lower, Physiolpgy, however, can prove with certainty, by experiments and 



