MATERIA MEDI'CA., 415

Materia Medica writers relieving only difeafes of the kid-neys. There is evidence of many Aftringents, befides rheUva Urft, being in the lift of Diuretics. A Phyfician wrotea Dictation, publifhed forty years ago, entitled, DsCalcuhAjlritigentibus curando , and I do not doubt but Aftringentsmay Sometimes promote this evacuation. I am told thatSiorck, in a late book, his Annus Medicus, recommends feve-ral Aftringents, in obftinate cafes of the Colica Piflonum,which fufficicntly fhews the uncertainty of the operation ofany medicine.

The operation of Diuretics does not depend on theirchanging the confiftence of our fluids, and I have no doubtin faying, that univerfally they a£t either by a ftimulus direct-ly applied to the kidneys, or to the parts confenting withthem. That the kidneys may be affefted by confent, ap-pears from there being a copious flow of limpid urine inhyfteric paroxyfms, in the fame manner as nephritic affec-tions caufe vomiting. It is from afting in the inteftines thatpurgatives, 1 imagine, exert their diuretic power, at leaftitis very doubtful if it be not fo, fince ftones in the kidneyscaufe Colics. Commonly, and perhaps properly, the fti-mulus of Diuretics is fuppofed of a faline nature ; but Iwould by no means confine it to this. Any Acrid will do,and there is Acrimony of an oily kind, and others withwhich we are not acquainted.

As to their general effefts:

1. They evacuate water from the blood-veflels, and bythe evacuation cauling an abforption, water accumulated inany quantity and ftagnating in the cavities. Hence theyare fuppofed to cure Dro'pfy, but their ftimulus is generallybut gentle, and we fucceed lei's often than we would with orimagine.

2. They evacuate with the water, the faline, putrefcentparts of our blood, and hence all Diuretics are Antifcorbu-tic ; and the contrarv.

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3. With thefe Diuretics wafh out all the extraneous bo-dies in the feroiity. Ilence they may be ufeful in evacuatingevery fort of Acrimony.

If their operation were certain, this clafs of medicineswould be of infinite advantage; nay, they may often be fowithout any fenfible effeft, for every Diuretic is a Diaphore-tic. In order to expede their operation, it is always properto throw in much water, which may run off by the feroustxcretorie's. The only exception to this is the cafe of

Dropfy,