THE IMPORTANCE OF THE SENSE OF SMELL

We have spent so much time on visual and tactual sensations because they represent the two senses which have been investigated most thoroughly on the physical and biological side. We know not only just what these groups of sensations are psychologically but how they are physically and biologically produced. Vision has another claim to careful study. It, along with audition, is known as a higher sense and is used more by civilized man than the lower senses of touch, taste and smell. We depend upon our eyes and ears as guides throughout all of our practical life and they are the two senses which have the highest biological development. Aside from their original function of orientation, civilization has forced them to serve two still higher purposes. Our eyes and ears are responsible both for the language which we use in conversation and for our two special forms of culture—art and music. We have no highly developed gustatory or olfactory art and although both of these senses are very important in our daily lives, we never use them as conscious means of communication. Yet viewed in relation to the evolution of the race, smell is the most important of all our senses. In the extension of the olfactory organs of the reptile we find the first hint of the development of a brain. And in all animals which live on the land the sense of smell is highly specialized.

Fish have no real olfactory sensations. The piscatorial organ which corresponds to the mammalian nose is really an organ of taste. Even animals which spend the greatest part of their lives in the water—whales, dolphins and seals—have very rudimentary olfactory organs and probably no real sensations of smell. Birds, also, contrary to common opinion, have a very poor sense of smell and exceedingly efficient eyes. The power which is usually attributed to their olfactory sensitivity is actually due to their extraordinarily keen sight. It has been proven by experiments that if a decaying animal carcass is carefully concealed carrion birds will pass directly by it without pausing to investigate. In all animals, however, who habitually live upon the ground, olfactory experiences are remarkably numerous and varied. It is easy to verify this fact by observing the behavior of insects and any four-footed mammals, especially dogs. But it is hard to believe that human beings are equally sensitive to odors. Yet they can be.

The human olfactory sense has been extensively investigated but at the present time no one has been able to state the exact number of smells which the human nostrils are capable of detecting. The chief difficulty lies in the fact that while the tactual and visual senses, for example, are physically limited, new odorous stimuli are being discovered every day. Each slightly different chemical compound produces a new odor and each new species of plant life carries its own typical smell. Already there is reasonable experimental ground for assuming that there are sensations from all of the other sense departments put together.

There are two principal reasons why we are generally unaware of this wealth of olfactory experiences. The first is that man habitually walks on two feet so that his nose, compared to that of other mammals, is very far from the ground and smells have a tendency to cling to the ground. Consequently, those smell stimuli which do reach his nostrils are very weak by the time they arrive there and are, therefore, generally ignored in favor of the more insistent visual and auditory tactual stimuli. In the second place, the most frequent and the strongest odors we experience we customarily ascribe to our sense of taste. We speak of the taste of our food when we are actually referring to its smell.

It is very easy to prove by experiment how limited is our sense of taste but we even have a very strong hint of the fact during our everyday life, or rather during that part of our everyday life when we are afflicted by a severe cold in the head. At such times we think that even the most savory meal has very little taste. Yet common sense should tell us that our tongues, which in adult life contain almost all of the sense organs of taste, are not seriously impaired by a bad cold. We should know that it is our noses, in which the olfactory organ is situated, which are really affected. It is the sense of smell which we habitually confuse with that of taste which is weakened. It is not entirely out of commission, however. There is a small passage at the back of the mouth, leading to the nose, of which we are disagreeably conscious when we choke. In swallowing, air laden with odorous particles is pushed up through this passage, the posterior nares of the nostrils are immediately stimulated and smell is experienced. This arrangement is quite evident to us when we take medicine which has a particularly disagreeable odor. Holding the nose helps a great deal until the dose is actually swallowed. If you should continue to hold your nose and, instead of swallowing, rinse your mouth thoroughly, you would be surprised to find how very little unpleasant “taste” the medicine contained. A rather agreeable sweetness might be all that remained.