THE INDIVIDUAL SENSES SEPARATELY CONSIDERED.

SECTION IV. OF THE SENSE OF SMELL.

HAVING, in the preceding chapter, treated of our perceptive powers in general, I proceed to describe the particular senses with which we have been endowed. Proceeding from the simpler to the more complex, I shall examine, in order, smell, taste, hearing, touch and sight.

The organ of smell is situated in the back part of the nostrils. It is composed of thin laminæ of bone, folded together like a slip of parchment, over which the olfactory nerve is spread, covered by the ordinary mucous membrane which lines the mouth and posterior fauces. It is so situated that the whole surface of the organ is exposed to the current of air in the act of inspiration.

In those animals which seek their prey by scent, this organ is found larger, exposing a greater amount of surface to the air, than in those which pursue their prey by sight. The perfection in which this sense is enjoyed by some of the lower animals has always been a subject of remark. A dog will track the footsteps of his master through the streets of a crowded city, and, after a long absence, will recognize him by smell as readily as by sight or hearing.

When we are brought near to an odoriferous body, we immediately become sensible of a knowledge, a feeling, or a

particular state of mind. If a tuberose is brought near a person who has never smelled it, he is at once conscious of a form of knowledge entirely new to him. If we do not, by our other senses, know the cause of the sensation, we have no name for it, but are obliged to designate it by referring to the place where we experienced it. If, by our other senses, we have learned the cause of the sensation, we designate it by the name of the object which produces it. Were the perfume of a rose present to me for the first time, and did I not see the flower, I could give to it no name. As soon as I have ascertained that the perfume proceeds from the rose, I call it the smell of a rose.

We thus see clearly that from this sense we derive nothing but a sensation, a simple knowledge, which neither gives us a cognition of anything external, nor teaches us that anything exists out of ourselves.

The exercise of this sensation is either agreeable, indifferent or disagreeable. The perfume of flowers, fruit, aromatic herbs, &c., is commonly pleasant. The odor of objects in common use is generally indifferent. The odor of putrid matter, either animal or vegetable, is excessively disagreeable. In general, it may be remarked that substances which are healthful for food are agreeable to the smell; while those which are deleterious are unpleasant. final cause of this general law is evident, and the reason why the organ of smell in all animals is placed directly over the mouth. Odors of all kinds, however, if they be long continued, lose their power of affecting us. We soon

become insensible to the perfume of the flowers of a garden; and men, whose avocation requires them to labor in the midst of carrion, after a short time become insensible to the offensive effluvia by which they are surrounded.

Pleasant odors are refreshing and invigorating, and restore, for the time, the exhausted nervous energy. Offen

sive odors, on the other hand, are depressing to the spirits, and tend to gloom and despondency. The former of these effects is alluded to with great beauty in the well-known lines of Milton:

"As when to them who sail

Beyond the Cape of Hope, and now are past
Mozambique; off at sea, north-east winds blow
Sabean odors from the spicy shore

Of Araby the blest; with such delay

Well pleased, they slack their course, and many a league,
Cheered with the grateful smell, old Ocean smiles."

Paradise Lost, Book 4, lines 159-165.

Concerning the manner in which this sensation is produced, I believe that but one hypothesis has been suggested. The received opinion is that what is called effluvia, or extremely minute particles, are given off by the odorous body, that these are dissolved in the air, and brought in contact with the organ of this sense in the act of breathing. That this may be so is quite probable. It is, however, destitute of direct proof, and is liable to many objections. It is difficult to conceive how a single grain of musk can, for a long time, fill the area of a large room with ever so minute particles, without visible diminution of either volume or weight. Until, however, some better theory shall be presented, we seem justified in receiving that which even imperfectly accounts for the facts in the case. Still, we are to remember that it is merely a hypothesis, to be abandoned as soon as better explanation is established by observation.

any

From what has been already remarked, it must be, I think, evident that the sense of smell gives us no perception. It is the source of a simple knowledge which alone would never lead us out of ourselves. This sensation clearly gives us no notion whatever of the quality which produces

it, nor have philosophers ever been able to determine what that quality is. It is possible that the suggestion of cause `and effect might indicate to us the probability of a cause, but the sense itself would neither awaken this inquiry nor furnish us with the means of answering it.

Does the sense of smell furnish us with any conception? By conception, I mean a notion of a thing, such as will enable us, when the object itself is absent, to make it a distinct object of thought. Thus I have seen a lily; I can form a distinct notion of its form and color, and I can compare it with a rose, and from my conceptions point out the difference between them. I could describe this lily, from my conception of it, so that another person could have the same notion of it as myself. Were I a painter, I could express my conception on canvas. Now, is there a similar power of forming a conception of a smell? Can I form a distinct notion of the smell of an apple or a peach, and can I compare them together, or describe them by language, or in any other manner transfer my conception to another? So far as I can discover, from observing the operation of my own mind, all this is impossible. After having smelled an odorous body, I know that I should be able to recognize that particular odor again. I cannot form a conception of the smell of a rose, but I know that I could, if it were present, immediately recognize it and distinguish it from all other odors. Beyond this I am conscious of no power whatever.

This, however, I am aware, is but the experience of a single individual. Other persons may be more richly endowed than myself. I have frequently put this question to the classes which I have instructed, and I find the testimony not altogether uniform. Some few young gentlemen in every class have assured me that they had as definite a conception of a smell as they had of a color or a form. The greater

part, however, have agreed with me that they had no power to form the conception in question.

It has, very probably, occurred to the reader that the words, "the smell of a rose," convey two entirely different meanings; the one objective, the other subjective. The "smell of a rose" may designate a peculiar feeling or knowledge existing in my mind, or it may designate the unknown cause of that feeling. Thus, when I say the smell of a rose is sometimes followed by fainting, I mean the sensation produced in the mind. I say the apartment is filled with the smell of a rose. I here mean the unknown quality existing in the rose. Both of these expressions I suppose to be correct, and in harmony with the idiom of the English language. The same ambiguity exists in all the terms commonly used to designate sensations. Thus, the taste of an apple, heat, cold, sweet, sour, and many others, admit of a similar twofold signification.

Chemical philosophers, aware of this ambiguity in language, have wisely introduced a new term, by which, in a particular case, this difficulty may be obviated. Observing that the term "heat" may signify a certain feeling in my mind, as well as the unknown cause of that feeling existing in a burning body, and as they were continually treating of the one, and almost never of the other, they have designated the two ideas by different words. Retaining the term heat to signify the sensation of a sentient being, they use the word "caloric " to designate the unknown cause of the sensation. Every one must perceive how much definiteness the use of this term has added to this branch of philosophical inquiry.

REFERENCE.

Reid's Inquiry, chapter 2, the whole chapter.