Smell has been defined as “taste at a distance,” and it is obvious that these two senses not only form a natural group, but are clearly associated in their physical action, especially in connection with the perception of the flavor of food.  The sense of odor gives us information as to the quality of food and drink, and more especially as to the quality of the air we breathe.  Taste is at the gateway of the alimentary canal, while smell acts as the sentinel of the respiratory tract.  Just as taste and flavor influence nutrition by affecting the digestive process, so the agreeable odors about us, even those of the perfumes, play an important part in the economy of life.

324.  The Sense of Sight.  The sight is well regarded as the highest and the most perfect of all our senses.  It plays so common and so beneficent a part in the animal economy that we scarcely appreciate this marvelous gift.  Sight is essential not only to the simplest matters of daily comfort and necessity, but is also of prime importance in the culture of the mind and in the higher forms of pleasure.  It opens to us the widest and the most varied range of observation and enjoyment.  The pleasures and advantages it affords, directly and indirectly, have neither cessation nor bounds.

Apart from its uses, the eye itself is an interesting and instructive object of study.  It presents beyond comparison the most beautiful example of design and artistic workmanship to be found in the bodily structure.  It is the watchful sentinel and investigator of the external world.  Unlike the senses of taste and smell we seem, by the sense of vision, to become aware of the existence of objects which are entirely apart from us, and which have no direct or material link connecting them with our bodies.  And yet we are told that in vision the eye is affected by something which is as material as any substance we taste or smell.

[NOTE.  “The higher intelligence of man is intimately associated with the perfection of the eye.  Crystalline in its transparency, sensitive in receptivity, delicate in its adjustments, quick in its motions, the eye is a fitting servant for the eager soul, and, at times, the truest interpreter between man and man of the spirit’s inmost workings.  The rainbow’s vivid hues and the pallor of the lily, the fair creations of art and the glance of mutual affection, all are pictured in its translucent depths, and transformed and glorified by the mind within.  Banish vision, and the material universe shrinks for us to that which we may touch; sight alone sets us free to pierce the limitless abyss of space.”—­M’Kendrick and Snodgrass’s Physiology of the Senses.]

Physicists tell us that this material, known as the luminiferous ether, permeates the universe, and by its vibrations transmits movements which affect the eye, giving rise to the sensation of light, and the perception of even the most distant objects.  Our eyes are so constructed as to respond to the vibrations of this medium for the transmission of light.