Part 38 (2/2)

Why do persons of firm health and vigorous const.i.tutions need less clothing than those who are feeble? What is a general practice among infirm persons? What would be more judicious? 582. Why should the surplus heat be removed equally from all parts of the system? What is said respecting currents of air from small apertures?

_Observation._ Currents of air that impinge upon small portions of the body, as from small apertures, or from a window slightly raised, should be avoided. They are more dangerous than to expose the whole person to a brisk wind, because the current of air removes the heat from the part exposed, which disturbs the circulation of blood and causes disease, usually in the form of ”colds.” For the same reason, it is not judicious to stand in an open door, or the opening of a street.

583. _The system suffers less when the change of temperature is gradual._ The change in the production of heat, as well as in the evaporation of fluids from the system, is gradual when not influenced by foreign causes. This gradual change is known under the name _acclimation_. By this means the body is enabled to endure tropical heat and polar cold. Owing to this gradual adaptation of the system to different temperatures, we can bear a greater degree of heat in the summer between the tropics, than in the winter under the polar circles. On the other hand, we can endure a greater degree of cold in winter and in the arctic region, than in the summer and in equatorial countries.

584. The sensation of heat which would be oppressive in a mild, warm day of January, would only be grateful in July, and a degree of cold which could scarcely be endured in August, would not be uncomfortable in December. The changes of season in our lat.i.tude prevent the disagreeable and perhaps fatal consequence that would follow, if no spring or autumn intervened between the severity of winter's cold and the intensity of summer's heat. During the transition periods, the const.i.tution is gradually changed, and adapted to bear the extremes of temperature without suffering. The amount of heat generated in the nutrient capillary vessels, is likewise diminished or increased as the temperature of the season becomes greater or less.

583. In what manner should change of temperature take place, to be adapted to the body? How is the body enabled to endure tropical heat and polar cold? State some of the effects of the gradual adaptation of the system to different temperatures. 584. What is said relative to a warm day in winter? To a cold day in summer? What is said of the changes of seasons in our lat.i.tude? What effect on the const.i.tution during spring and autumn? What change in the amount of heat generated?

585. But, on the contrary, we cannot suddenly pa.s.s from one extreme of temperature to the other with impunity. Let an inhabitant of Quebec suddenly arrive in Cuba in February, and he would suffer from languor and exhaustion; after becoming acclimated to this tropical climate, let him suddenly return to Quebec in January, and the severity of the weather would be almost insupportable.

_Observations._ 1st. Experience shows that heated rooms, as well as tropical climates, lessen the generation of heat in the body, and likewise the power of resisting cold. It would be idle for the merchant from his warehouse, or the mechanic from his heated shop, to attempt to sit on the box with a coachman, with the same amount of clothing as his companion, who is daily exposed to the inclemency of the weather.

2d. ”It is the power of endurance of cold at one period, and the absence of its necessity at another, that enables animals, in their wild and unprotected state, to bear the vicissitudes of the seasons with so little preparation in clothing, and so little real inconvenience.”

585. What effect on the system has a sudden transition from a cold to a warm climate? What does experience show? Why do wild animals bear the vicissitudes of the seasons with so little preparation in clothing?

CHAPTER XXIX.

THE VOICE.

586. The beautiful mechanism of the vocal instrument, which produces every variety of sound, from a harsh, unmelodious tone, to a soft, sweet, flute-like sound, has, as yet, been imperfectly imitated by art. It has been compared, by many physiologists, to a wind, reed, and stringed instrument. This inimitable, yet simple instrument, is the _Larynx_.

587. Incidentally, the different parts of the respiratory organs, as well as the larynx, are subservient to speaking and singing. The tongue, nasal pa.s.sages, muscles of the fauces and face, are agents which aid in the intonation of the voice.

ANATOMY OF THE VOCAL ORGANS.

588. The LARYNX is a kind of cartilaginous tube, which, taken as a whole, has the general form of a hollow, reversed cone, with its base upward toward the tongue, in the shape of an expanded triangle. It opens into the pharynx, at its superior extremity, and communicates, by its inferior opening with the trachea. It is formed by the union of five cartilages, namely, the _Thyroid_, the _Cricoid_, the two _A-ryt-enoid_, and the _Ep-i-glottis_. These are bound together by ligaments, and moved by muscles.

586. What is said of the structure of the vocal instrument? With what instrument have physiologists compared it? What is the vocal instrument called? 587. What organs are called into action in speaking beside the larynx? 588-596. _Give the anatomy of the vocal organs._ 588. Describe the larynx. Name the cartilages that form the larynx.

589. The THYROID CARTILAGE is the largest of the five, and forms the prominence in the front of the neck, called _Pomum A-dami_, (Adam's apple.) It is composed of two parts, and is connected with the bone of the tongue above, and with the cricoid cartilage below.

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