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degree of heat, without the least injury; but then they are lefs irritable.

SPALANZANI obferved the newts bury themselves in the earth, and become torpid, in the month of October, before the thermometer in the fhade falls to 54 degrees; and that they re-appear in the month of February, though at that time it freezes during every night, and not uns frequently during the day the thermometer is many degrees below 54.

"What is the reason," enquires this excellent obferver, that these animals revive in SPRING, when the cold is more intense; and fink into torpidity at a much less degree of cold in the AUTUMN?"

I will folve this problem, by observing that in AUTUMN a very great ftimulus is required to act upon the fibre of these animals, exhaufted as it has been by the heat of the fummer; but in SPRING, the least stimulus, the least increase of heat, is sufficient to put the fibre into action, its irritability having accumulated during winter in confequence of the absence of the common ftimuli."

Thus precifely is it with the vegetable tribe, for they fleep in winter, and are awakened by the vernal fun; but die, if too powerful a heat be fuddenly applied. ::

On

On this principle we may account for the deftruction of plants by blight in fummer; for unless there be frost at night there is no blight; and it may be remarked, that the blight does not take place during the action of the froft, but at the rifing of a cloudless fun.

Hence it is that our garden crops, fuch as French beans and peas, which usually suffer most by blight after a frosty night in summer, suffer no injury if they are watered immediately before the rifing of the fun, because the evaporation abates the heat.

The effects of winter are therefore very great in cold climates, because the accumulation of the irritability is in proportion to the abstraction of the ftimulus of heat.

In LAPLAND corn ripens in 60 days, whereas in FRANCE it requires 120 or 160 days. The truth of what is here advanced may be proved by expofing vegetables alternately to heat and cold: it is furprising how much their growth and the power of vegetation is increased. But in these experiments care must be taken to vary the temperature by degrees; because the irritability accumulating in the fibre by the abstraction of the heat, a very small quantity of this ftimulus then applied is fufficient to exhauft it entirely, or to destroy it.

SECT.

SECT. XXXVIII.

THE MANNER IN WHICH COLDS AND INFLAMMA

TORY FEVERS ARE PRODUCED.

On going into a cald bath, fuppofe at 33 degrees of heat on Fahrenheit's fcale, the action of the capillary arteries of the skin is diminished, or ceafes for a time. Hence lefs or no blood paffes these capillaries, and pale. nefs fucceeds. But foon after emerging from the bath, a more florid colour, and a greater degree of heat, is generated on the skin than was poffeffed before immerfion; for the capillary arteries, after their quiefcent itate, occafioned by the want of ftimulus, become more irritable than ufual to their natural ftimuli, owing to the accumulation of irritability, and hence a greater quantity of blood is transmitted through them, and in consequence a greater degree of heat fucceeds. Befides the quiefcence of the minute veffels of the lungs, there are many other fyftems of veffels which become torpid from their irritative affociations with those of the skin.

From the quiefcence of fuch extensive systems of veffels as the capillaries of the skin, and the minute veffels of the lungs, with their various abforbent feries, a great accumulation of irritability is occafioned; part of which is again expended in the increafed exertion of all these veffels, with an univerfal glow of heat in confequence of this exertion, and the remainder of it adds vigour to both the vital and voluntary exertions of the whole day.

If the activity of the fubcutaneous veffels, and of those with which their actions are affociated, was too great before cold immersion, as in the hot days of fummer, by which the irritable principle was previously diminifhed, we fee the cause why the cold bath gives fuch present strength; namely, by stopping the unnecessary activity of the fubcutaneous veffels, and thus preventing the too great exhauftion of the irritable principle.

In those constitutions where the degree of inirritability, or of debility, is greater than natural, the coldness and paleness of the skin, with the quick and weak pulse, continue a long time after the patient leaves the bath; and the subsequent heat approaches by unequal flufhings, and he feels himself disordered for many hours. Hence the bathing in a cold spring of water, where the heat is

but

but 48 degrees of Fahrenheit's thermometer, much difagrees with those of weak or unirritable habits of body; who poffefs fo little of the irritable principle, that they cannot without injury bear to have it diminished even for a fhort time; but who can nevertheless bear the more temperate coldnefs of Buxton baths, which is about 80 degrees of heat, and which strengthens them, and makes them by habit lefs liable to great quiefcence from fmall variations of cold, and thence lefs liable to be difordered by the unavoidable accidents of life. Hence it appears, why people of these inirritable conftitutions, which is another expreffion for a defective irritability, are often much injured by bathing in a cold spring of water; and why they should continue but a very short time in baths which are colder than their bodies; and fhould gradually increase both the degree of coldness of the water, and time of their continuance in it, if they would obtain fa- . lutary effects from cold immerfions †.

One RICHARD EDWARDS, of Liverpool, a healthy young man, twenty-eight years of age, with black hair and a ruddy complexion, went into fome fresh water, which was about the temperature of mild weather, viz. about 40 degrees by the thermometer. He continued

+ Dr. DARWIN. Vide note, page 413.

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