eruptive fevers, as the Small-Pox and Measles, alfo at this time prevail.

In the fecond, from a vigorous circulation and prevalence of the paffions, the constitution is liable to Pleurifies, Inflammations of the Lungs, and Confumption; but where tempe rance is obferved, and the vital parts are naturally found, this may be deemed the most healthy period of human life: It re lieves, or cures fome diseases and occafions few; for then Scrophulous Complaints, and habitual Convulfions have been known to difappear.

In the last period, the limbs become contracted and paralytic; the fight, hear ing, and intellect are impaired, from a rigi dity of the folids, and defect of circulation. The paffions fubfide, and every vital principle is at laft extinguished.

From what has preceded, it follows, that animal bodies continue to grow fo long as the blood's circulating power is greater than the refiftance of its veffels; and when

T

when there is an exact balance between the two, animal growth will be totally at a ftand. As age gradually hardens the veffels, they are, at last an over-match for the force of the Heart; old Age commences, the circulation languishes, and at last the animal dies.

Perhaps, however, very few can properly be faid to die of mere old age; for even the life of old Parr might probably have been still prolonged, had he not suddenly changed his air, and manner of living.

Here we may obferve, that by a kind of fatal Neceffity, animal bodies are worn out and destroyed by that very cause which constitutes the principles of life, namely, the circulating power of the blood; and confequently, the number of years to which men may attain, will probably be in proportion to the velocity of the Pulfe; if fo, it will then follow, that fuch a particular state of conftitution as produces the greatest de

gree of ftrength and vigor in youth, is not A a 2 moft

moft likely to prolong life; but on the contrary, that those of weak folids, and delicate habits in their earlier ftate, grow old more flowly than others; and if the Viscera are found, become for a time, more strong and healthy from the very effect of age.

The gradual, and mechanical change thus produced by age, from infancy to the latest period of life, is continually introducing a fucceffion of new fenfations, and confequent ideas, which alter the bias, and diverfify the operations of the mind; totally abolishing fome paffions, and putting other's in their place. Thus, vanity, indifcretion, and the immoderate love of pleafure, are the unripe product of youth; whilft aufterity, fcrupulous caution, avarice, and a contempt of pleasure are the furly off fpring of old age,

"Behold the Child, by Nature's kindly law,
"Pleas'd with a rattle, tickled by a straw:

"Some livelier play-thing gives his youth delight,

A little louder, but as empty quite

Scarfs

"Scarfs, Garters, Gold, amufe his riper stage,
"And Beads and Prayer-books are the toys of age:
"Pleas'd with this bauble ftill, as that before;
"'Till tir'd he fleeps, and Life's poor play is o'er."
A. POPE.

Particular habits acquired by long custom are also found infenfibly to gain afcendency over the most intelligent minds, and to produce very extraordinary effects, to the benefit or prejudice of health; as well as the moral or immoral tendency of the paffions.

The Body and Mind are so disposed by the Author of nature, that they cannot act separately, but are mutually affected by the fole mediation of the Nerves, from impreffions alternately made on the one or other; fo that the feveral paffions can only produce their effects, whether good or bad, by increafing or diminishing the influence of these fenfible organs on the bodily fyftem.

When any injury is done to the brain or nerves by external violence, intoxication, or febrile delirium; the diftinct exercise of

the mental faculties immediately vanish, and the whole animal machine is thrown into disorder. On the contrary, although the bodily organs remain perfect and duly perform their functions; so powerful are the mental affections, that extreme terror, or exceffive joy will fuddenly disconcert the animal œconomy, and fometimes occafion faintings, convulfions, or death.

This evidently fhews, that many dange rous diseases may be produced fimply by impreffions made on the nervous fyftem, without any morbid change of the blood, except what arifes from the confequence of fuch external affections. It also appears, that those remedies which act by strengthning the bodily fyftem, of which the nerves. make fo confiderable a part, are of all others the best adapted for the cure of their difeases; but what relates to this circumftance, as well as the power of fympathy between the corporeal organs, and that fentient prin