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 latitude? What effect on the constitution during spring and autumn? What change in the amount of heat generated? -=-=-=-=-=-=-=-=-=-=-=-= 585. But, on the contrary, we cannot suddenly pass 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 _Lar´ynx_. 587. Incidentally, the different parts of the respiratory organs, as well as the larynx, are subservient to speaking and singing. The tongue, nasal passages, muscles of the fauces and face, are agents which aid in the intonation of the voice. ANATOMY OF THE VOCAL ORGANS.