Part 55 (2/2)
860. _The condition of the cuticle modifies the impression made upon the cutaneous nerves._ 1st. When the cuticle has become thick and hard, like horn, as on the inside of the mason's hand, it enables him to ply his tools without much suffering, because the thickened cuticle diminishes the impressions made upon the nerves.
How is it demonstrated? 858. How is the influence of the blood upon the skin further demonstrated? How should circulation be restored to limbs frozen or severely chilled? What should be avoided? 859. Show how the quality of the blood influences sensation. 860. Give the 1st condition of the cuticle that influences the impressions made on the cutaneous nerves.
861. 2d. When the cuticle is very thin and delicate, as on the hand of the lady who is unaccustomed to manual labor. Let her pursue some manual employment for several hours, and the extreme tenuity, or thinness of the cuticle, will not protect the nerves and parts below from becoming irritated and inflamed.
862. 3d. When the cuticle is removed by blistering or abrasion, the pain indicates that the naked nerves are too powerfully stimulated by the contact of external bodies. 4th. When the cuticle is coated with impurities, blended with the secretion from the oil-glands, the sensibility of the skin is lessened.
863. _The sensibility of the cutaneous nerves is modified by being habituated to impressions._ If, for example, an individual should immerse his feet in moderately warm water, at first it might induce a smarting sensation; in a short time, the nerves would not only become habituated to the warm water, but its warmth night be considerably increased. The same results follow, if an individual is exposed to a cold element. The impressions at first are highly disagreeable; but as soon as the nerves become accustomed to the surrounding atmosphere, it may impart the most agreeable sensations.
_Ill.u.s.tration._ 1st. Let a person from the tropical regions go to a colder climate, and the cool mornings of the latter will at first affect him unpleasantly; but, after a few days' exposure to the cooler air, the sensation will be far from disagreeable.
2d. Let a person enter a room moderately heated; gradually increase the temperature, until it attains extreme summer heat; not only the cutaneous nerves, but the whole system, become habituated to the high temperature. From these facts we learn that the sensations, are not always a correct index of the real temperature. A well-adjusted thermometer will indicate it with unerring certainty.
861. The 2d condition. 862. The 3d and 4th condition. 863. Show how habit influences the sensibility of the cutaneous nerves. Give ill.u.s.tration 1st. Ill.u.s.tration 2d.
864. _Touch is modified, in a high degree, by education._ Thus the blind, whose ”windows of the soul” are closed to the beauties of the external world, cultivate this sense to such a degree that they can distinguish objects with great accuracy. And the rapidity with which they read books prepared for their use, is a convincing proof of the niceness and extent to which the cultivation of this sense can be carried.
_Ill.u.s.trations._ 1st. The cloth-dresser, by the aid of this sense, distinguishes the quality, as well as the slightest difference of texture, in the different pieces of cloth.
2d. The miller, from a similar education, quickly detects the quality of flour or meal, by permitting it to pa.s.s between his fingers. The difference in the texture of cloths, or the quality of the flour, would not be distinguished by an individual whose tactile sense had not been trained to make nice comparisons.
864. Is this sense susceptible of improvement? What persons cultivate it to a high degree? Give ill.u.s.tration 1st. Ill.u.s.tration 2d.
CHAPTER XLII.
SENSE OF TASTE.
865. The chief organ of TASTE is the upper surface of the tongue; though the lips, the palate, the internal surface of the cheeks, and the upper part of the oesophagus, partic.i.p.ate in this function.
ANATOMY OF THE ORGANS OF TASTE.
866. The tongue is a double organ, composed chiefly of muscular fibres, which run in almost every direction. The two sides are so perfectly distinct, that sometimes, in paralysis, one side is affected, while the function of the other remains perfect. It possesses great versatility of motion, and can be moulded into a great variety of shapes. In articulation, mastication, and deglut.i.tion, the tongue is an auxiliary to other organs.
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