The limits of this article prevent our noticing other objections which have been urged against the theory just described, but the facts it rests upon can only be overturned by opposing facts which have never yet been produced. It is certain that carbonic acid is produced during respiration, that its production is always attended with heat, that pure (arterial) blood is capable of absorbing a greater portion of heat than impure (venous) blood, and that the temperature of any part of the body is according to the supply of blood which it receives; an inflamed part, becoming very hot, and a limb in which the circulation has been stopped by a bandage becoming cold. These facts taken together sufficiently prove the truth of the conclusion that has been drawn from them, and which we have above very briefly illustrated. It remains to say a few words on the manner in which the body is relieved of its superabundant heat, and enabled to bear such high degrees of temperature as mentioned in the former paper. Franklin was the first who gave a rational explanation of the phenomenon. He observed that the evaporation of a small quantity of a liquid from the surface of any substance would reduce the temperature of a very large body. If we place a little ether on our hand, and allow it to evaporate, we shall soon become sensible how much cold may be produced in this way. Wine-coolers are formed on this principle: they are made of porous earth, through which the water they contain oozes very gradually, and is evaporated by the heat of the air: this cools the liquid within, and of course the decanter of wine contained in it. Now, perspiration cools the body in a similar manner. If any person looks closely at the fleshy part of his hand, he will observe that the minute ridges which lie nearly parallel to each other are covered with an innumerable number of small pores, through which the perspiration may be seen issuing when the hand is warm. From microscopic observations it is calculated that the skin is perforated by 1000 of those pores, or holes, in every square inch, and that the whole surface of the body therefore contains not less than 2,304,000 pores! When the body is heated to a certain degree, the fluid portions are all directed to the skin, and escape gradually through these pores in the form of perspiration, and the cooling power thus produced is capable of immediately removing the superabundant heat. The moment perspiration broke out on the bodies of the experimenters who ventured into the heated oven, all sense of pain was removed; and in many fatal disorders to which man is subject, the first symptom of returning health is a similar occurrence. We may add, that a common cold is the effect of the perspiration being suddenly checked, and that the health of the body depends on the minute pores we have referred to being kept open and in action. J. S. D.