The skin contains more than two million openings, which are the outlets of an equal number of sweat-glands. The human skeleton consists of more than two hundred distinct bones. An amount of blood equal to the whole quantity in the body passes through the heart once every minute. The full capacity of the lungs is about three hundred and twenty cubic inches. About two-thirds of a pint of air is inhaled and exhaled at each breath in ordinary respiration. The stomach daily produces nine pounds of gastric juice for digestion of food; its capacity is about five pints. There are more than five hundred separate muscles in the body, with an equal number of nerves and blood-vessels. The weight of the heart is from eight to twelve ounces. It beats one hundred thousand times in twenty-four hours. Each perspiratory duct is one-fourth of an inch in length, of the whole about nine miles. The average man takes five and one-half pounds of food and drink each day, which amounts to one ton of solid and liquid nourishment annually.

A man breathes eighteen times a minute, and three thousand cubic feet, or about three hundred and seventy-five hogsheads of air every hour of his existence. ______