VII

SENSE CULTURE. VISION AND ADDITION

The early cultivation of the senses essential to the proper conduct of the study and practice of medicine-General remarks on the five senses-The visual sense-Seeing with the mind's eye Quickness of visual perception; its importance to the physician; how to exercise it-The auditive sense-Exercise of the mind's ear for correct interpretation of heart and respiratory sounds, etc.-Music as an aid to the cultivation of audition.

THE importance of early beginning the cultivation of the senses, in order to bring them up to a high degree of efficiency for guidance in his present labors, is soon realised by the diligent student who, later, profits so much by this culture in his medical practice and social relations. How to cultivate the five senses, for his present and future purposes, with the least labor and the most pleasure, is now to be told as briefly as the subject may allow. However, a few preliminary remarks on the senses in general are needful toward the elucidation of such questions as are likely to arise in the mind of the listener.

Each wonderfully designed human sense apparatus necessarily has, in each individual, its own peculiarities of construction and action, as, otherwise, all mankind would see, hear, feel, smell, and taste with an equal degree of precision. But if such were the case, there probably

would be little interchange of ideas or spicy expression of like or dislike for particular objects, and possibly as little observation of the phenomena of nature which so teems with variations in the animal and vegetable kingdoms. Although it is mainly upon the animal man that attention is now more particularly fixed, a glance, for comparison, may be cast profitably at the most glaring sense peculiarities of some of the lower creatures.

Of visual peculiarities, it has been asserted that certain nocturnal animals, such as bats and owls, are not able to distinguish colors because of the absence, in their retinæ, of those minute conical bodies that are believed to be essential to the perception of tints, whilst the eyes of some diurnal birds, that hunt bright colored insects, are very richly supplied with retinal cones. Extremes like these need not be regarded as imperfections, for they are really variations needful to the habits of those creatures. It has also been suggested by some observers, and denied by others, that congenital "color blindness" in man is due to a greatly disproportionate number of retinal rods and a paucity of cones. The subject is well worthy of further investigation. The specialisation of color tints is extremely delicate among the fair sex, particularly in adolescence; and great advantage has been taken of this knowledge in the arts. In the visual sense of man, the variations, known to exist entirely in the refractive apparatus of the eye and to interfere with the right appreciation of certain objects seen, are many but nearly all remediable. The auditive sense of many of the higher vertebrata is

well known to be much more acute and alert than that of man, though in construction their middle and internal ears bear some resemblance to those of man, particularly the beasts that are much preyed upon and must be quickly aware of the approach of an enemy in good time to flee. It is said that aquatic animals have no middle ear, which would be useless to them because, in their case, sound waves are easily transmitted from the ambient to the labyrinthic liquid. The sounds inaudible to the unaided human ear are the extremely shrill and the extremely grave. The physicist's whistle is thus unheard. The hum of a swarm of gnats is scarcely audible, and the bellowing of the whale is so grave that it has no effect whatever on the ear-drum of man. That leviathan has been seen, not heard, calling to his mate. In the first or second case the drum-membrane cannot be made to vibrate naturally with sufficient rapidity, that is, more than thirty-five thousand times per second, and in the third case the drum-head is not adapted to the very slow vibrations, less than two two per second, requisite to render audible these gravest of sounds.

The tactile sense is possessed in a higher or lower degree by superior as well as inferior organisms. In these, however, it will require long and persistent researches to determine its diffusion; though it is already known to exist in some plants, notably the carnivorous whose peculiar leaves so quickly enfold lured insects and remain tonicly closed until the bodies are consumed. The many tentacles of the sea-anemone serve to feel, select, and convey its prey

to the ample oral aperture. The taction of the oyster or clam is sufficient to cause the creature to close its shell on the near approach of an unwelcome intruder. The long antennæ of crustaceans serve well the purposes of touch, and even give warning of approaching prey or danger. This sense is well developed in many insects whose antennæ are as long fingers. In birds, the sense of touch is exquisitely delicate, particularly in the beak near the tip of which have been found well-organized tactile corpuscles. In mammals its variations are without end, up to man. The wings of the common bat are said to be so richly endowed with tactility as to enable the animal to "sense objects without actual contact." The larger beasts touch mainly with the end of the nose, the lips, and the tip of the tongue; the sense is comparatively blunt in other parts. The stiff antennæ-like hairs near the angles of the mouth, notably of the felidæ, are delicate tactile organs at the base of each of which is a touch corpuscle. The end of the elephant's proboscis is possessed with such tactile delicacy that with it, the huge monster is able to pick up a single straw.

The olfactive sense of some of the vertebrates is much keener than that of man, though not so delicate; but that sense, in certain tiny creatures, is very highly developed, as in those insects that have to see extremely small objects with their thousand facetted eyes and their ocelli, while they "find their food more by smell than sight," such as the ants who have only fair vision, but very strong olfaction.

The gustative sense of beasts has been illustrated from very low forms up to domestic animals where it is strongest even to daintiness, as in the case of cats and dogs. In men, gustation is susceptible of great cultivation, but the greatest height of gustative delicacy is to be sought only in the better half of man.

In each order, genus, and species, including man, the senses are developed and varied in proportion to the needs of the creatures. These sensual variations, which are in no sense defects, are almost infinite.

It has long been observed that when one sense is impaired or destroyed, other senses acquire increased activity by way of compensation. For instance, in the case of the blind, the olfactive and auditive senses are much more alert than formerly, and tactile sensibility becomes very delicate even in the soles of the feet. A physician, who had lost his sight soon after entering upon the practice of his profession, determined to devote himself to teaching and became an accomplished quiz-master with a large following of pupils who took turns as his readers. He had a phenomenal memory, and such a great power of concentration of attention that after listening to the reading of a whole chapter he could repeat it word for word. He had so cultivated his auditive and tactile senses that sounds almost inaudible to others were distinctly heard by him and, bat-like, the slightest waves of air announced to him the approach of persons whom he was generally able to call by name, but it was mostly through the tone of voice that he distinguished individuals. He daily went