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fordid end, they often embrace deformity, disease, ignorance, peevishness, and every thing that is difgufting to the generous mind. The confequences do not affect them only, but the public. Men of rank, in all nations and governments, are the natural guardians of the state. For these important purposes, their minds fhould be noble, generous, and bold; and their bodies fhould be ftrong, masculine, fit to encounter the fatigues of and to repel every hoftile affault that may be made upon their country. But when men of this description, whatever be their motives, intermarry with weak, deformed, puny, or dif eafed females, their progeny muft of neceflity degenerate. The strength, beauty, and symmetry of their ancestors, are, perhaps, for ever loft. What is still more to be regretted, debility of body is almost invariably accompanied with weaknefs of mind. Thus, by the avarice of one individual, a noble and generous race is completely deftroyed. By reverfing this conduct, it is true, the breed may again be mended; but to repair a fingle breach, many generations, endowed with prudence and circumfpection, will be requifite. A fucceffive degeneration, however, is an infallible confequence of imprudent or interested marriages of this kind. One puny race may for fometime be fucceeded by another, til at last their conftitution become fo feeble, that the animals lofe even the faculty of multiplying their fpecies.

SECT. XVIII.

OF TEMPORARY EXHAUSTION.

THE fibres as well as the nerves are under the fame laws, being fubject alike to exhaustion, which is either TEMPORARY, OF IRREPARABLE.

In the ftate of temporary exhauftion, the fibre fails for want of IRRITABILITY. The application of the ordinary stimulus, while it is in this ftate, will not make it contract. It is only by little and little that the fibre recovers its IRRITABILITY. This truth, I dare venture to fay, is as new as it is ftriking, and it unfolds a vaft number of phænomena hitherto unexplained.

Let us obferve, for example, the motion of the heart; the heart contracts from the ftimulus of the blood, and impels the blood through the arteries; it then again dilates, and the blood enters. But the heart does not contract itself immediately upon the first impreffion of the blood. Its IRRITABILITY having been leffened by the preceding contraction, it requires half, or three quarters of a fecond, before the IRRITABILITY of the heart fhall have been recruited to fuch a degree that the ftimulus can act upon it.

Thus alfo during the operation of an emetic or cathartic, the ftomach and bowels are alternately

in a state of excitement and repofe. And thus the moft violent pains and labour of a parturient woman, if not effectual for the expulfion of the offspring, ceafe for a time, and are then renewed. Thus likewife all the appetites are liable to fits, returning after ceffation at stated periods; if it be hunger, at the diftance of fome hours; if it be fever, it may be explained on the fame principle; that is to fay, any ftimulus which is always prefent, and continually acting upon the fibres, produces no fenfible effect till the exhaufted irritability of the fibre fhall have accumulated afresh.

You can fcarcely touch the leaf of the mimofa, or fenfitive plant, fo flightly as not to make it close. The large rib which runs along the middle of the leaf, ferves as an hinge on which the two halves of the leaf turn on being touched, till they stand erect, and by that means meet one another. The flighteft touch gives this motion to one leaf; if a little harder, it gives the fame motion to the leaf oppofite. If the touch be ftill rougher, the whole arrangement of leaves on the fame rib clofe in the fame manner. If it be fronger fill, the rib itfelf moves upwards towards the branch on which it grows. And if the touch be yet more rough, the very branches fhrink up towards the main ftem.

In Auguft, one of thefe plants growing in a pot was put into a carriage. The motion of the carriage caused it to fhut up all its leaves, and the effect of this great ftimulus was, that it did not again

expand its leaves for more than four and twenty hours. A TORPOR then enfued: for having opened their leaves, they clofed no more for three days and as many nights.-Being then brought again into the open air, the leaves recovered their natural motions, shutting each night, and opening in the morning, as regularly as ever.

All the periodical motions of animals, may be explained upon the fame principle; that is to fay, any ftimulus which is always prefent, and continually acting upon the fibre, produces no fenfible effect till the exhaufted irritability of the fibre fhall have been accumulated afresh. The periodical motions in organized bodies depend on the alternate exhaustion and accumulation of the irritability of the fibre. A temporary exhauftion of the irritability of the hedyfarum gyrans, is produced by the heat of the fun and by electricity. The electrical fluid exhausts in like manner the irritability of the mimofa.

SECT.

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