. Essentials de biologie a présenté des problèmes. La biologie. Le SYSTÈME NERVEUX ET LES ORGANES DE S1':SNG 407 ces projections sur le haut et l'arrière du cadre de la langue, sont situés les organes du goût. Ces organes sont appelés papilles. Chacune des papilles est composé d'une collection de cellules nerveuses en forme de fusée, chaque cellule à sa pointe extra-fin avec un hairUke projection. Ces cellules envoyer vers l'intérieur à d'autres cellules, des fibres Les fibres de qui finissent par atteindre le cerveau. Les cellules sensorielles sont entourés d'un certain nombre de protection de cellules qui sont disposés en couches à leur sujet. Ainsi, l'orgue en longi- tudinal sect

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. Essentials of biology presented in problems. Biology. THE NERVOUS SYSTEM AND ORGANS OF S1':NSE 407 these projections on the top and back part of the tongue, are located the organs of taste. These organs are called taste buds. Each taste bud consists of a collection of spindle-shaped nerve cells, each cell tipped at its outer end with a hairUke projection. These cells send inward fibers to other cells, the fibers from 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 longi- tudinal section looks somewhat like an onion cut lengthwise. How we Taste. — Four kinds of substances may be distinguished by. Section of circumvallate papilla. 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 perceived by cells near the tip of the tongue, sour substances along the sides, and salt about equally all over the surface. 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 vege- tables. 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. / 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 sniS so as to draw in more air over the olfactory cells. The Organ of Hearing. — The organ of hearing is the ear. In the flsh, frog, and reptile, the outer ear, so prominent in man, is entirely lacking. The outer ear consists of a funnel-like organ composed largely of cartilage w

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• bookcentury1900
• bookdecade1910
• booksubjectbiology
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