This tendency of mercury readily accounts for the bad effects of taking cold under its influence. It is easy to conceive that the bad effects of checking perspiration will be most felt when, to use a common expression, the pores are most open, that is, when the secretion by the skin is most copious; for the greater the quantity of fluid thus discharged, the greater inconvenience is to be expected from suddenly checking its secretion. Hence also the danger of suddenly checking perspiration, when, by exercise or external warmth, it is rendered more copious than usual. Such is the admirable constitution of our bodies, that means are provided for more or less successfully counteracting the operation of every thing which tends to injure them. If a thorn or any other extraneous body is introduced under the skin, inflammation and suppuration spontaneously arise, by which the offending cause is expelled. If a poisonous substance is received into the stomach, the action of vomiting is frequently excited, or if it passes into the bowels, nature still endeavours to carry it off by an increase of the peculiar motion of the intestines, and of the secretion from their surface; so in the case before us, the morbid fullness which would in every instance arise, when perspiration suffers a check, is generally prevented by the sympathy which subsists between the skin and several other secreting organs, in consequence of which, as soon as a check is given to the action of the former, some one of the latter, which secrete a similar fluid from the blood, is called into more vigorous action, and what should have passed by the skin is thrown off by the kidneys or bowels, sometimes by the glands of the nose, throat, and lungs, occasioning what we call a _cold_. This substitution of one excretion for another, if I may use the expression, is particularly apt to occur under the use of mercury, and seems to arise from the nature of this medicine being so stimulating that we cannot retain it in the system: if one vent is denied it, it quickly finds another. Hence it is that people under the effects of mercury are so subject to an increased secretion from the kidneys and intestines, and from the glands of the mouth and throat.