injures the brain, and leads especially to weakness of the heart by interfering with its supply of nervous force. Many cases of cancer of mouth and throat are believed to have resulted from tobacco smoking. Opium, for its benumbing influence upon the nerves, is used by large numbers of persons, especially in Oriental lands. Its continued use deranges all the digestive processes, disorders the brain, and weakens and degrades the character. Like alcohol, it produces an intolerable craving for itself, and the strongest minds are not proof against the deadly appetite. "Self-control versus Appetite. Man is a bundle of appetites. Every organ, every cell even, craves its appropriate stimulus. Animals under natural conditions gratify the appetites as they arise only to that extent which is healthful for the whole body. Man alone, whose highly developed brain is overlord to the rest of his system, permits an unwholesome indulgence of appetite to interfere with this general well-being. Alcohol, opium, and their like are far from being the only substances whose excessive use injures the organism and degrades character. Children are often allowed to indulge a natural fondness for sweets to an extent which is ruinous to digestion; for sugar, which is a useful and necessary food in suitable quantities, becomes in larger ones a poison to the system. Boys pampered with dainties from infancy logically infer that a fancy for cigars or beer may be similarly gratified. Appetite for even the most wholesome food may be in excess of bodily needs, and the practice of gluttony is certain to derange nutrition. "A child should be early taught that because he 'likes' a certain article of food he should not therefore continue to eat it after natural hunger is satisfied, or at times when he does not need food; while to persist in eating or drinking that which experience, or the advice of those competent to judge, has taught him to be harmful, should be regarded as unworthy a rational being. "These are but illustrations of the manifold forms of intemperance which work untold harm to the physical and moral natures. There seems no possibility of improvement to our race except as the young are led to recognize the manliness and dignity of controlling one's appetites." -MACY, Physiology. XXXVI. THE SENSES Touch. In animals having a hard outside covering, such as certain worms, insects, and crustaceans, minute hairs, which are sensitive to touch, are found growing out from the body covering. At the base of these hairs are found nerve cells which send a nerve fiber inward to the central nervous system. Organs of Touch. In man, the nervous mechanism which governs touch, is located in the folds of the dermis or in the skin. Special nerve endings, called the tactile corpuscles, are there found. They are inclosed in a sheath, or capsule, of connective tissue. Inside is a complicated nerve ending, and nerve fibers are sent inward to the central nervous system. The number of tactile corpuscles present in a given area of the skin determines the accuracy and ease with which objects may be known by touch. Nerves in the skin; a, nerve fiber; b, tactile papillæ, containing a tactile corpuscle; c, papillæ containing blood vessels. (After Benda.) If you test the different parts of the body, as the back of the hand, the neck, the skin of the arm, of the back, or the tip of the tongue, with a pair of open dividers, a vast difference in the accuracy with which the two points may be distinguished is noticed. On the tip of the tongue, the two points need only be separated by 24 of an inch to be so distinguished. In the small of the back, a distance of two inches may be reached before the dividers feel like two points. Temperature, Pressure, Pain. The feeling of temperature, pressure, and pain, the latter only in part, are determined by organs in the skin. Physiologists believe, however, that these organs are distinct from the apparatus which distinguishes touch. Taste Organs. The surface of the tongue is folded into a number of little projections known as papillæ. These may be more easily found on your own tongue if a drop of vinegar is placed on its broad surface. In the folds, between these projections on the top and back part of the tongue, are located the organs of taste. These organs are called taste buds. Taste Cells A, isolated taste bud, from whose upper free end project the ends of the taste cells; B, supporting or protecting cell; C, sensory cell. Each taste bud consists of a collection of spindleshaped nerve cells, each cell tipped at its outer end with a hairlike projection. These cells send inward fibers which ultimately reach the brain. The sensory cells are surrounded by a number of protecting cells which are arranged in layers about them. Thus the organ in longitudinal section looks somewhat like an onion cut lengthwise. How we Taste. - Four kinds of substances may be distinguished by the sense of taste. These are sweet, sour, bitter, and salt. Certain taste cells located near the back of the tongue are stimulated only by a bitter taste. Sweet substances are per Papilla Taste Buds: -Wall ceived by cells near the tip of the tongue. A substance must be dissolved in fluid in order to be tasted. Many things which we believe we taste, are in reality perceived by the sense of smell. Such are spicy sauces and flavors of meats and vegetables. This may easily be proved by holding the nose and chewing, with closed eyes, several different substances, such as an apple, an onion, and a raw potato. Nerves Section of circumvallate papilla. Smell. The sense of smell is located in the membrane lining the upper part of the nose. Here are found a large number of rod-shaped cells which are connected with the forebrain by means of the olfactory nerve. In order to perceive odors, it is necessary to have them diffused in the air; hence we sniff or draw in more air over the olfactory cells so as to bring more odoriferous particles to them and thus to distinguish the odor. The habitual use "Effects of Alcohol upon Taste and Smell. of drinks containing alcohol, of tobacco, and of very strongly flavored foods is found to dull the sense of taste, and by alcohol, at least, the olfactories are rendered less acute."-MACY, Physiology. In a fish, THE ORGAN OF HEARING.-The organ of hearing is the ear. frog, or reptile, the outer ear, so prominent in man, is entirely lacking. The outer ear consists of a funnel-like organ composed largely of cartilage which is of use in collecting sound waves. This part of the ear incloses the auditory canal which is closed at the inner end by a tightly stretched membrane, the tympanic membrane. We have seen the tympanic membrane of the frog on the outer surface of the head. The function of the tympanic membrane is to receive sound waves, for all sound is caused by vibrations in the air, these vibrations being transmitted, by the means of a complicated apparatus found in the middle ear, to the real organ of hearing located in the inner ear. MIDDLE EAR.-The middle ear in man is a cavity inclosed by the temporal bone, and separated from Section of ear, showing auditory canal, middle ear, internal ear, and Eustachian tube. the outer ear by the tympanic membrane. A little tube called the Eusta chian tube connects the inner ear with the mouth cavity. By allowing air to enter from the mouth, the air pressure is equalized on the ear drum. For this reason, we open the mouth at the time of a heavy concussion and thus prevent the rupture of the delicate tympanic membrane. Placed directly against the tympanic membrane and connecting it with another membrane, separating the middle from the inner ear, is a chain of three tiny bones, the smallest bones of the body. The outermost is called the hammer; the next the incus or anvil; the third the stirrup. All three bones are so called from their resemblances in shape to the articles for which they are named. These bones are held in place by very small muscles which are delicately adjusted so as to tighten or relax the membranes guarding the middle and inner ear. THE INNER EAR.-The inner ear is one of the most complicated, as well as one of the most delicate, organs of the body. Deep within the tem poral bone there are found two parts, one of which is called, collectively, the semicircular canal region, the other the cochlea or organ of hearing. Both of these organs consist of membranous bags lying in a fluid which partially fills the bony cavity which incloses them. These membranous structures themselves also contain a fluid. The semicircular canals are connected with the cochlea on one side, and are separated from the middle ear only by a membrane and the fluid which surrounds them. There are three semicircular canals, delicate membranous bags lying in a watery fluid and surrounded by bone. It has been discovered by experimenting with fish in which the semicircular canal region forms the chief part of the ear, that it has to do with the equilibrium or balancing of the body. We gain our knowledge of our position and movements in space by means of the semicircular canals. That part of the ear which receives sound waves is known as the cochlea, or snail shell, because of its shape. This very complicated organ is lined with sensory cells provided with cilia. The cavity of the cochlea is filled with a fluid; this fluid presses against the membrane and separates the inner from the middle car. It is believed that somewhat as a stone thrown into water causes ripples to emanate from the spot where it strikes, so sound waves, transmitted by the bones of the middle ear to the membrane guarding the entrance to the inner ear, are transmitted by means of the fluid filling the cavity to the sensory cells of the cochlea (collectively known as the organ of Corti) and thence to the brain by means of the auditory nerve. THE CHARACTER OF SOUND.-When vibrations which are received by the ear follow each other at regular intervals, the sound is said to be musical. If the vibrations come irregularly, we call the sound a noise. If the vibrations come slowly, the pitch of the sound is low; if they come rapidly, the pitch is high. The ear is able to perceive as low as thirty vibrations per second and as high as almost thirty thousand. The ear can be trained to recognize sounds which are unnoticed in untrained ears. CARE OF THE EAR.- -Some of the cells lining the cavity of the outer ear secrete a bitter substance called wax. This wax, which aids in keeping the canal of the outer ear moist, also aids in keeping foreign matters, especially living insects, out of the ear. In removing wax or dirt no sharp pointed instrument should be used. Inflammation of the ear should be treated by a doctor, as at such times pus may gather in the inner ear in sufficient quantity to rupture the tympanic membrane. In serious cases, the bone around the inner ear may become diseased and the brain affected. The ear should be protected against sudden loud sounds, such sounds tending to break the tympanic membrane. When the ear is sensitive to cold or dampness, a small wad of cotton may be inserted when going out of doors. This should always be removed upon entering the house. THE EYE. -The eye or organ of vision is an almost spherical body which fits into a socket of bone, the orbit. What might be the function of this |