At each beat each ventricle pumps on rather more than six ounces (say fourteen tablespoonfuls) of blood. The elastic aorta and the pulmonary artery are full, and resist the pumping of more liquid into them, just as an elastic bag filled with water could only have more sent into it by force; to get more in one would have to stretch the bag more. The resistance opposed by these arteries to receiving blood from the heart has been measured in some of the lower animals, and calculations made from them to man. According to these the work which the left ventricle does every day, sending ounces of blood seventy times a minute into the aorta, is enough to lift one pound 325,584 feet high; and the work done by the right ventricle would lift one pound 108,528 feet. The work done daily by the ventricles of the heart together is equal to that required to raise one pound 434,112 feet from the earth's surface, or, what comes to the same thing, more than 193 tons one foot high.

What parts of the heart does the blood enter during the pause? What is the condition of the ventricles as regards fullness at the end of the pause? What is done by the auricular contraction? What is the chief use of the auricles?

How much blood does each ventricle pump out at every beat? What resists the ventricular emptying? Illustrate. How much work does a man's left ventricle do daily? How much the right?

If a man weighing 165 pounds climbed up a mountain 2644 feet high the muscles of his legs would probably be greatly tired at the end of his journey, and yet in lifting his body that height they would only have done as much work as his heart does every day without fatigue in pumping his blood.

No doubt the fact that more than half of every round of the heart's activity is taken up by the pause during which its muscles are relaxed and its cavities filling with blood, has a great deal to do with the patient and tireless manner in which it pumps along, minute after minute, hour after hour, and day after day, from birth to death.