The phenomenon which is popularly known as “reaction,” and which occurs after both hot and cold baths, is a most remarkable one, and seems to show that our bodies resent any interference with their function. Thus experiments have shown that if the temperature of a healthy man be raised or depressed by any artificial means, such as hot or cold baths, the subsequent reaction in the direction of the depression or exaltation of the temperature is such that the mean temperature of health is accurately maintained. A German observer, Jurgensen, found by a series of accurate observations on a patient who submitted to a series of baths of a temperature of 50° Fahr., each bath lasting twenty-five minutes, that notwithstanding the rapid abstraction of heat, which gave rise to shivering, lasting for several hours, the diminution of bodily temperature which occurred during the bath was followed, after an interval of four or five hours, by an elevation which precisely compensated it, so that the mean normal temperature was maintained in spite of the interference of the physiologist. It will have been observed that the ultimate result of both hot and cold bathing, if conducted in moderation, is about the same, viz., an increased circulation of blood through the skin. In both cases also, the combustion going on within the body is increased, as evidenced by the escape of an increased quantity of carbonic acid from the lungs. In the case of the cold bath, this increased combustion is due to the stimulating effect of the cold water, while in the hot bath it is due to the artificial heat facilitating the natural combustion processes of the body. The effects of the hot and cold bath upon the combustion processes going on in the body may, not inaptly, be compared to the effect produced upon a furnace by the hot and cold blast, both of which encourage combustion and increase the heat given off by the furnace; but the hot blast so facilitates combustion that the same work is done by its aid, with an expenditure of 2-1/2 tons of coal, that is done by the cold blast with an expenditure of 8 tons of coal. If we want a fire to burn well, we have several courses open to us; the first is to poke it, which may be regarded as simple stimulation; the second is to supply it with a cold blast, in which case we supply large quantities of oxygen, but at the same time counteract the heating effect by the coldness of the blast. By employing a hot blast, the combustion is facilitated without any counteracting chilling. By each of these methods we hasten the ultimate extinguishing of the fire, unless fresh fuel be added. The employment of the hot blast entails the most economical use of the fuel.