Yet exposure to cold is one of the most common causes of various complaints. As a rule it is true that there is danger from sudden vicissitudes of temperature, although the proposition requires limitation. No peril need attend a change from a hot to a cold temperature if the power to evolve heat inherent in the system be entire and active and persistent, not lessened by any of those circumstances which have the effect of weakening it, such as local disease, and fatigue. Cold is dangerous, not especially when the body is hot, but when it is cooling after being heated. At such times taking a large draught of cold water, or cooling the body suddenly some other way might cause death immediately; if not, an inflammation of some internal part of the body might arise. Every thing that has the effect of weakening the system and so diminishing the power of evolving heat, favors the morbific effect of cold, and is a predisposing cause of disease. The most common of these debilitating circumstances are fasting, evacuations, fatigue, a last night’s debauch, excess in venery, long watching, much study, and rest or inaction immediately after it, or after great exercise. The faculty of evolving heat is weak in old persons and in the newly born, and these are often the victims of the power of cold. The bad effects of cold depend very much upon the duration of the sensation. Even slight feelings of chilliness, if long protracted, are apt to terminate in some form of disease. Cold is more likely to prove injurious when it is applied by a wind or currant of air, and the injurious operation of cold is augmented when it is accompanied with moisture—wetness is the worst way in which cold can be applied. The contact of wet or damp clothes with the skin, both increase and prolong the sensation of cold. A foggy atmosphere is more prejudicial than a clear one of the same temperature. While we are asleep, also, our power of resisting the effects of cold is diminished. The power of habit enables a person to resist the effect of cold, and we may sometimes turn our knowledge of it to good account in gradually fortifying the system against the influence of cold that cannot be avoided. But we must not, while we fear to render our children effeminate by over care and much clothing, run into the opposite extreme and endanger their health by exposure. The process of hardening is doubly dangerous when it is attempted with children who were originally delicate, and should never be tried on any child or any person who is unsound, who shows any signs of present or approaching disease, or any marked predisposition to future, and especially to scrofulous disease. An abiding sense of chilliness must never be permitted even when we are endeavoring to accustom a child to cold. If they can be kept in the cold air, and at the same time be kept feeling warm either by exercise, diversion of the mind, or by clothing, the result as regards the health is good.