SCHOOL IN THE OPEN.

Star (Christchurch), Issue 18786, 15 June 1929, Page 20 (Supplement)

SCHOOL IN THE OPEN.

STUDIES IN THE GREAT OUT-OF-DOORS.

(By

J. J. S. Cornes,

8.A., B.Sc.

The “Star” has arranged with Mr J. J. S. Cornes, 8.A., B.Sc., tc write a series of illustrated articles which will give teachers arid • others a fuller appreciation of the Great Out-of-Doors. They will deal with various aspects of plant and animal life, as well as with inanimate nature. Questions and material for identification will be welcomed.

SIGHT AND HEARING.

CCXCIII. Ever since I caught the “ talkie ” bug I have thought a lot of sight and hearing, and our other senses. The Organs of Sense. Our wonderful sense-organs. slowly evolved, began as simple sensitive patches in the skin, which, m th>2 course of millions of years, have grown into elaborate organs. They are the sentinels of the commonwealth of cells. For ages theirs was the vital function of locating food and announcing danger. Now, in man, they are the ; chief channels of those glimpses of nature which the mind unites in the marvellous structure of modern science. Pain. The skin, to begin with, is crowded with little organs of sense. Nerves from the great centres branch out in every direction, and the fine twigs at : last end in sensitive bulbs underneath the skin. The most numerous of these are for the purpose of announcing “ pain.” We speak of pain as something in the body-machine which we could very well spare. But while it is more terrible to stand by helpless and see men suffer, than to see men die, and while humanity is more anxious to see agony relieved than life prolonged, yet pain on the whole and altogether is perhaps a benevolent, and the only possible institution, as guide along sort of pathway by which we have evolved. Pain announces some danger which, if it were not thus indicated by the ringing of the bell in the brain, would not be noticed, and might become fatal. Touch. Little bulbs, espegialh* numerous on the palm-side of the fingers, minister to the sense of touch. Others feel cold, and a different set experience heat. There are other nerve endings again for the sense of pressure. These senses are all localised in different little areas along the skin. Taste. Other sensitive bulbs, which line part of the mouth, arp the receiving organs for the sense of taste. Little oval bodies stand up like a close regiment of diminutive soldiers on the upper surface of the tongue. Each of the internal cells of these “ taste-buds ” ends in a hair-like process, and these processes touch the nerves which convey their particular stimulation to the brain. The tip of the tongue is richer in the little bulbs that perceive sweet things, the back part in the means of recognising bitterness. Smell. Substances must be in a liquid form to announce themselves to taste. For the sense of smell, on the other hand, they have to be broken up into very fine particles like a gas. Nerves from the olfactory centres in the brain branch out in the membrane which lines the upper part of the nasal cavities, and this membrane includes numerous sensory nerve-cells which act as

sentinels against dangers which announce themselves in the air. An odorous body is one which gives off minute particles of its matter into the air. The sense of smell was once of the gravest importance in the animal

economy, and even in men it is so highly developed that they can detect a speck of musk diluted in eight millio.i times as much air. A very strong offensive substance like mercapton can be “ sensed ” even if there is only one grain to twenty-five billion times as much air. In man, however, the sense of smell is degenerating, and many individuals have it very feebly. Vision. Most important of all the senses is 1 that of vision, for nearly ail the ideas of things in the mind of the ordinary person are visual images. The essential part of the mechanism of this more complex sense is the eyeball, and the nerve which goes thence to the sight-centre in the brain. The eye is i a camera, by no means faultless as

merely such, yet a camera of most remarkable description. It is a roundish ball made of dense and strong fibrous tissue, opaque for five-sixths of its surface, but transparent for the one-sixth which bulges out in front, as the cornea. To the interior of the cornea, separated from it by a watery fluid, there is a delicate curtain which hangs over the transparent “ window ” in front-of it. and forms the variously coloured iris. This curtain is a wonderful arrangement for adapting the eye to the intensity of light which falls upon it. Fibres of muscle are so ingeniously distributed in it that it can almost clo.fi the opening in strong light, or open it wide when the light is fainter. The photographer's iris-diaphragm is but a poor imitation of it. Moreover, it contains pigment-cells which may be crowded when the light is strong, or fewer when the eye wants as much light as possible. So we get the black eyes (eyes rich in pigment, to mitigate the light) of the dwellers in southern Europe, and the blue eyes (with little pigment) of the dweller in darker northern in New Zealand every intermediate shade and combination c_ them! Behind the circulai window, the pupil, is the crystalline lens, which, un-

In front the cornea window closes the front of the anterior chamber, filled with watery humour, and backed by the coloured curtain, the iris, in whose centre is the round opening, the pupil —which looks black because we are looking into the dark camera-bellows beyond. Behind, then, is this round “bellows” filled with “glassy” humour. Entering from behind is the optic nerve, which is distributed to the internal lining, the retina, the sensitised plate of our camera. The next wall of the eyeball, with nourishing blood vessels, in the choroid (black) and the outermost wall the firm protective schlerotic (white).

like any lens of man’s making, can be altered in curvature by fine muscles so as to focus itself for any distance. Other muscles and tendons are attached to the outside of the eyeball, and they automatically, turn it in the direction we want. Some men of science (as well as the spectacle-mak-ers) we have said, have found many defects in the eye—yet none of them, thinking of the unconscious agencies which have built up this wonderful camera, and work it, even clean it,

automatically every moment of our waking lives, is disposed to cavil. But the most wonderful part is the “ sensitive plate ” at the back of the eyeball, the dark “ bellows-chamber,” into which light is focussed through, that black-seeming “ aperture,” the pupil. A semi-transparent membrane, the retina, lines three-fourths of the interior of the eyeball (which is filled with fluid) and it is particularly well developed at one spot, the “ yellowspot.” the real seat of distant vision. On this yellow spot in each eye the rays of light form an inverted image of the .object at which we are looking, j The stereoscope enables us to underi stand how the images of the two eyes ; are blended, and how they enable us to see (nature in depth as well as in length and breadth. Vision is so marvellous that we cannot expect to understand it yet awhile. How do we distinguish the three primary colours? There seems to i be chemical action in the wonderful rod-and-cone nerve cells of the retina.

But is there a separate chemical for each colour? Is colour-vision connected with one or more fine chemicals which may be lacking in ‘‘colour-blind” people? However thafli may be, the nerve-lining closes Tip at the back of the eyeball, and, as the optic nerve, conveys the images of things in some way to the conscious centre. What pre cisely travels along the nerve we cannot say. but to imagine that an image or picture is conveyed is to be but a child again, and think, as we then thought, that words travel along a telegraph wire. Hearing.—No less remarkable is the organ of hearing. From the outer ear, protected against adventurous insects by wax secreted by its glands, a narrow channel, about an inch long, conducts waves of sound to the real ear. At the outer end of this passage the sound-waves beat . upon a sensitive drum, the tympanum, a membrane of most ingenious construction. This membrane must not have a period of vibration of its own. It must respond read il}’, and yet impartially, to every sort of wave that impinges on it. It is therefore so constructed that each part of it has a different period of vibration, and it is further '‘damped” by a little bone prising against it on the other side. The pressure on the air on the inside of the drum, which must alter with changes of pressure outside, is regulated by a channel (the Eustachion tube) running to it from the roof of the mouth). Three little bones (the hammer, anvil and stirrup) convey the vibrations of the drum to another drum, which is stretched across the entrance to the real ear inside the skull. As the waves of sound impinge on the tympanum and set it vibrating, the three little i bones work together and repeat the vi- J brations on the second drum, the, ‘oval j window”. Beyond this is a coiled shell which contains the real organ of hear ing—a large number of hair-cells (the ‘‘organs of Corti”) interlacing with the fine fibres of the auditory nerve The vibration of the ‘‘oval window” .agitates the fluid inside this organ, and the hair cells communicate this movement to the nerves, which then convex it to the brain Once more we have a mechanism full of ingenuity in every part, in which fresh research will still repeal new wonders, and to which a brief description like this seems almost unjust. When I think of the wonderful elec-

trie pick-up and speaker-diaphragm of the sound-picture amplifier, and what they can do, I almost worship American genius and perseverance; but when I reflect that my own ears and eyes are the standard, after all, by which I judge or condemn, and that my own ear-drums had “straight line amplifica- . tion without peak-frequency due to natural resonance” before talkies w r ere thought of, I bow to my mother who made me, without such bother and big words about it. (To be continued next Saturday.)