due power, a moderate ftimulus is requifite to ftir up all the actions of life. Old age, on the contrary, owing to a deficiency of excitability, requires a great deal of ftimulus; it becomes enfeebled by too little, and quickly overfet by more

*

In one word, EXCITEMENT, the effect of stimulating powers, when of a proper degree and fuited to the perfon, conftitutes firm health; when either exceffive or deficient, proves the occafion of weakness and disease.

* This verifies the old adage, "MILK is the food of infancy, and WINE of old age." What calumnies have not been thrown out against JOHN BROWN for this doctrine. If low living and farving are reprobated for the facts and reasons that presently will be affigned, why, therefore, fhould he be called a friend to intemperance? On the contrary, he only approves and tries to ad ́just the proper standard, condemning all extremes, and advifing the mean under which VIRTUE takes her poft. If he has any ways erred in this difficult but honourable attempt, as he certainly did not err wilfully, I know not why he fhould be held up as criminal, or cenfured with greater afperity than the exploded theories of BOERHAAVE or CULLEN. This knowledge will affuredly, as Dr. BEDDOES justly obferves, become a part, and the most important part, of education. Phyfiological ignorance is the most abundant fource of our fufferings; every perfon accustomed to the fick, must have heard them deplore their ignorance of the neceffary confequences of those practices, by which their health has been deftroyed; and when men shall be deeply convinced, that the eternal laws of nature have connected pain and decrepitude with one mode of life, and health and vigour with another, they will avoid the former, and adhere to the latter. And as actions are often named immoral from their effects, felf love, or the enjoyment of health, are so far the fame. Nor is this fort of morality likely to terminate in itself; but the habit of acting with thought and refolution, will extend from the felfifh to the focial actions, and regulate the whole tenour of life.

Π

SECT III.

OF EXTREME HEAT.

HEAT, which is neceffary, when moderate, to the production, growth, and the vigour* of animals and vegetables, may, like other ftimuli, have also a debilitating power; as must be obvious to every one who pays the least attention to the operations in nature. During the Scorching heats of fummer, especially at mid-day, all nature languishes, and her energy is loft. The plants,

* Some years ago I cut out, fays Dr. GARDINOR, the heart and part of the large veffels of a turtle, with a view to examine the structure of these parts, and the circulation of the blood in that animal. Having wiped off the blood and other moisture, the heart was wrapped up in a handkerchief; but engagements in the way of my profeffion obliged me to poftpone my curiofity till about fix or feven hours after it was cut out. When I examined it, there appeared not the leaft figns of life. It was much shrivelled and dried. But, by putting it into water, nearly milk warm, it plumped up, and some of its parts. acquired a tremulous motion. Laying it on the table, and pricking it with a large needle, it palpitated several times. The palpitations were renewed, as often as the needle was pushed into its fubftance, until it became cold, when it feemed to be infenfible to every ftimulus. But, after warming it again in the water, it recovered its irritability, and repeated its palpitations on the application of the needle. Though no movement could be excited in it by any ftimulus when cold, yet it moved several times after being macerated in warm This evidently fhews the neceffity of HEAT for maintaining the full powers of the contractile living principle. Vide Sect. IX. Part II.

water.

8

exhaufted

exhausted of their vigour, hang their heads; their foliage droops and among these the MIMOSA *, the DIONEA MUSCIPULA †, with the HEDYSARUM GYRANS, lofe their fenfibility and motion; whilft the various tribes of animals, panting for breath, feek fome cool retreat. Even in our northern latitude this cannot escape our notice; but to fee it in perfection we must vifit the more fultry regions of the south, where the African, patient of heat, is obliged to intermit his labour, whilst the inhabitants of more temperate climates, fuch as Italy and Spain, retire into fome dark recefs and fleep.

The learned profeffor BOERHAAVE gives us fome experiments, made by the celebrated FAHRENHEIT, with

* Senfitive plant.

In the DIONA MUSCIPULA, or fly-trap, there is a moft wonderful contrivance to prevent the depredations of infects: the leaves are armed with long teeth, and lie fpread upon the ground around the ftem. These are so irritable, that when an infect creeps upon them, they fold up, and crush, or pierce, the poor animal to death.

The leaves of the HEDYSARUM GYRANS, or whirling honeysuckle, are continually in fpontaneous motion; fome rifing and others falling; and others whirling circularly, by twifting their stems; this fpontaneous movement of the leaves goes on when the air is perfectly ftill. A particular account, with a good print of the HEDYSARUM GYRANS, is given by Monf. BROUSSONET, in a paper on Vegetable Motions, in the Hiftoire de l'Academie des Sciences, Ann. 1784, p. 609.

U 2

view to difcover the extent of heat living animals are able to endure.

A fparrow, fubjected to air heated to 146 degrees of Fahrenheit's thermometer, after fome ftruggles, died in lefs than feven minutes. A cat refifted this great heat fomewhat above a quarter of an hour; and a dog in about 28 minutes died, after discharging a confiderable quantity of a ruddy-coloured foam, which had fuch offenfive qualities as to throw one of the affistants into a fainting fit *.

Meffieurs DU-HAMEL and TILLET, having been fent into the province of Angoumois, in the years 1760 and 1761, with a view of endeavouring to destroy an infect which consumed the grain of that province, effected the fame by expofing the damaged corn in an oven, where the heat was fufficient to kill the infects without injuring the grain. This process was performed at Rochefoucault, in a large public oven; where, for economical views, their firft ftep was to affure themfelves of the heat remaining in it on the day after bread had been baked. This they did, by conveying in

* Vide the ftory of the hole at CALCUTTA, where a pungent fleam, like hartfhorn, is faid to have iffued from those who were at a distance from the

window.

a ther

a thermometer on the end of a fhovel, which, on being withdrawn, indicated a degree of heat confiderably above that of boiling water. But Monf. TILLET, conceiving that the thermometer had fallen many degrees at the entrance of the oven, and appearing under fome embarraffment on that score, a girl, one of the conftant attendants on the oven, begged that the might enter it, and mark with a pencil the height at which the thermometer ftood within the oven. The girl fmiled at M. TILLET's fears, and without hesitation entered the oven, and with a pencil, given her for the purpose, marked the thermometer, after staying two or three minutes at 100 degrees of Reaumur's fcale, or, to make use of a scale better known in this country, at near 260 degrees of Fahrenheit's. M. TILLET began to be anxious for this girl, and to entreat her speedy return, but the girl crying out, " She felt no great inconvenience," remained in her prefent fituation ten minutes longer; that is, near about the time when BOERHAAVE'S cat parted with her nine lives under a much less degree of heat. She then came out, her refpiration quiet, with a hurried pulse, and a complexion confiderably heightened.

After