174 ESSAYS ann OBSERVATIONS 
its purgative power is uncertain, for fome- 
times it has not the leaft effe@ of that 
kind. As it isa mere infipid earth, he 
rationally concludes it to be a purgative 
only when converted into a fort of neutral 
falt by an acid in the ftomach, and chat 
its effect is therefore proportional to the 
quantity of this ad@d. 
ALTHOUGH magnefia appears from this 
hiftory of it to be a very innocent medi- 
cine; yet, having obferved, that fome hy- 
pochondriacs who ufed it frequently, were 
fubject to flatulencies and f{pafms, he feems 
to have fufpected it of fome noxious qua- 
lity. The circumftances however which 
gave rife to his fufpicion, may very pofii- 
bly have proceeded from the imprudence 
of his patients, who, trufting too much to 
magnefia, (which is properly a palliative in 
that difcafe, ) and neglecting the affiftance 
of other remedies, allowed their diforder 
to increafe upon.them. It may indeed 
be alledged, that magnefia, as a purgative, 
is not the molt eligible medicine for fuch 
confiitutions, as they agree beft with thofe 
that ftrengthen, ftimulate, and warm ; 
which 
