_Observation._ When intending to ride in a cold day, wash the face, hands, and feet, in cold water, and rub them smartly with a coarse towel. This is far better to keep the extremities warm, than to take spirits into the stomach. 373. _Exercise promotes the circulation of the blood._ As the action of the muscles is one of the important agents which propel the blood through the arteries and veins, daily and regular exercise of the muscular system is required to sustain a vigorous circulation in the extremities and skin, and also to maintain a healthy condition of the system. The best stimulants to improve the sluggish circulation of an indolent patient, whose skin is pale and whose extremities are cold, are the union of vigorous muscular exercise with agreeable mental action, and the systematic application to the skin of cold water, attended with friction. -=-=-=-=-=-=-=-=-=-=-=-= 371. Why should the temperature of the body be equal? 372. Why should the skin be kept at its natural, as well as at an equal temperature? What practical observation when intending to ride in a cold day? 373. Why does exercise promote health? What are good stimulants for sluggish circulation in the indolent? -=-=-=-=-=-=-=-=-=-=-=-= _Illustration._ The coach-driver and teamster throw their arms around their bodies to warm them when cold. The muscles that are called into action in swinging the arms, force a greater quantity of blood into the chilled parts, and consequently, more heat is produced. 374. When a number of muscles are called into energetic action, a greater quantity of blood will be propelled to the lungs and heart in a given time, than when the muscles are in a state of comparative inaction. It is no uncommon occurrence, that before there is a proper expansion of the respiratory organs to correspond with the frequency and energy of the movements of the muscles, there is an accumulation of blood in the lungs, attended by a painful sensation of fulness and oppression in the chest, with violent and irregular action of the heart. This condition of the organs of the chest, called _congestion_, may be followed by cough, inflammation of the lungs, asthma, and a structural disease of the heart. 375. To avoid these sensations and results, when we feel necessitated to walk or run a considerable distance in a short time, commence the movements in a moderate manner increasing the speed as the respiratory movements become more frequent and their expansion more extensive, so that a sufficient amount of air may be received into the lungs to purify the increased quantity of blood forced into them. The same principles should be observed when commencing labor, and in driving horses and other animals.