"THE SENSES AND SENSE ORGANS."

Shannon News, 14 May 1926, Page 2

"THE SENSES AND SENSE ORGANS."

, W.E.A. LECTURE. Despite a streaming night there was a good attendance at the usual weekly lecture of the W.E.A. held in the Y.M.CA. Rooms on Tuesday. Tin' president, .Mr P. W. Goldsmith, was in the / chair. The lecturer explained that the brain as well as the nerve fibres were exceedingly well protected by nature against any interference from the outside world. The brain had the protection of the hair, the thick skin of the scalp, the bony box or skull, at least two thick membranes surrounding the brain itself, and as .though to make assurance doubly /sure, a fluid in .which the brain was suspended. All these coverings minimised shock or injury. Under these circumstances the only things that can happen to the brain are:— - (1) The dullest and feeblest .mechanical jars; (2.) Changes in the quantity and quality of the blood supply; (3) Currents running in through the different nerves.

In' dealing with (3) one had to. take note of the characteristic mark in "sensation." It is caused by a stimulus which is always some condition external to the nervous system, and operating on it from outside. Sensation is a response to. a stimulus, and is an elementary*mental process as it cannot be split up into anything simpler. A very young infant can have a "sensation," but later that sensation is accompanied by an "idea about" sensation and this "idea about" sensation is called perception. The nerves that carry the stimulus to the sense, organs are exclusive—the optic nerve is insensible to heat waves, while sensitive to light waves; the auditory nerve faJLs to respond : to light waves, but is "tuned up" for sound waves. Each selects from the outside world some one stimulus to which it responds exclusively, A sense organ is a portion of the body which has a high degree of sensitivity to its own. particular kind of stimulus. There is one thing a. sense Organ always must have—the termination of a sensory nerve—and in certain organs there are accessories which assist the sensory nerve to carry the stimulus to the organ. These accessory or sense cells are to be found in the eye, ear,- nose, and i\iouth and always in sheltered situations Nature has provided these sense cells with hair cells—full hairs which gather the waves—either of sound or light —and communicate with their respective organs. In the "semi-circular canals"—a part of the bony structure of tlu; inner ear, these hair cells sway with the rotary, movement of the head and so tend to establish and main tain equilibrium. Some people, through defective nerve 'response become nauseated when climbing a hill. In these cases the stimulus is deflected somewhere and the brain in attempting to recover from a wrong 1 sensation, creates that "sick", feeling. The lecturer gave in detail the kinds of sensations experienced by the sense organs of the eye, ear, skin, mouth, nose, and internal organs (lungs, blood vessels and alimentary canal). Are colours real, or are they only , mental facts? This question occasioned quite a long discussion at the close of the lecture. It would seem that those who claim that colours are only mental have a good case. Colour is caused by undulations or wavss of the ether. The soft green of the foothills is backed by the blue of Hie ranges behind them and these in turn are backed by the purple of the still more distant ranges. But as one approaches the hills, the blue and the purple disappear and become green. The colour is given by.the distance or the length of the undulations ot . the air.

The carolling of the lark up in what seems to he the blue sky is but the impacting of air vibrations upon the sense organ—the ear. Were colour a real existent thing then there should he no case of colour-blindness. So with the sense of smell. When one has a "cold in the head" the sense organ does not receive the sensation. Some persons also can a smell that is non-existent. Mr McArthur explained what is known as "Weber's Law," relative to added intensity of sensations. Experiments have shown that when one has a weight in one's hand l-17th ol the weight may be added before the increase is detected, unless the hearer sees the extra weight being put on. So with light sensations, this is 1/lOOth: muscle sensation l/17th, pressure *-rd, sound -Jrd. Sense of Taste—This is composed largely of odour. The taste, of food, etc!, is made up of the smell as well as of the taste for" if the nose be held while certain food substances are being taken, the taste is entirely obliterated. This is a good way to take castor oil. Sense of Smell.—Hienniug has demonstrated that there are six element ary odours:—(1) Spicy, (2) flowery, (3) fruity, {'i) resinous, (5). foul, (6) scorched. There are obviously many con mounds.

Pain.—This was shown to be the re- • sult of a high degree of intensity in a stimulus caused either by mechanical means or by irritant or inflammation. The sensory nerve normally responds to a certain intensity, but when this is greatly exceeded the nerve rebels. Pressure and heat and cold, when intense, have the same pain response. Light and sound sensations may be so intense as to cause pain. At the close of the lecture about 30 slides illustrative of the. subject,, were shown. The internal structure of the ear, the structure and accommodation of the eye, the tongue, the nerve end-

ings in the skin and the delicate and intricate apparatus of the oliactory organ. ,