o
spring or autumn intervened between the severity of winter's cold and
the intensity of summer's heat. During the transition periods, the
constitution 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.

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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?

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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."

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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?

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CHAPTER XXIX.

THE VOICE.

586. The beautiful mechanism of the vocal instrument, which produces
every variety of sound, from a harsh, unmelodious tone