114 THE CIRCULATION. 



28. Again, if we estimate the amount of blood expelled 

 by each contraction of the ventricles, at four ounces, then 

 the weight of the blood moved during one minute will 

 amount to eighteen pounds. In a day it will be about 

 twelve tons; in a year, four thousand tons; and in the 

 course of a lifetime, over one hundred and fifty thousand 

 tons. These large figures indicate, in some measure, the 

 immense labor necessary to carry on the interior and vital 

 operations of our bodies. In this connection, we call to 

 mind the fanciful theories of the ancients in reference to 

 the uses of the heart. They regarded it as the abode of 

 the soul, and the source of the nobler emotions bravery, 

 generosity, mercy, and love. The words courage and 

 cordiality are derived from a Latin word signifying heart. 

 Many other words and phrases, as hearty, heart-felt, to learn 

 by heart, and large-hearted, show how tenaciously these ex- 

 ploded opinions have fastened themselves upon our language. 



29. At the present time the tendency is to ascribe purely 

 mechanical functions to the heart. This view, like the 

 older one, is inadequate; for it expresses only a small part 

 of our knowledge of this organ. The heart is unlike a 

 simple machine, because its motive power is not applied 

 from without, but resides in its own substance. Moreover, 

 it repairs its own waste, it lubricates its own action, and it 

 modifies its movements according to the varying needs of 

 the system. It is more than a mere force-pump, just as 

 the stomach is something more than a crucible, and the 

 eye something more than an optical instrument. 



30. The Arteries. The tube-like canals which carry 

 the blood away from the heart are the arteries. Their 

 walls are made of tough, fibrous materials, so that they 

 sustain the mighty impulse of the heart, and are not rup- 

 tured. In common with the heart, the arteries have a del- 



28. Amount of blood expelled ? Theories of the ancients ? 



29. The tendency at the present time ? Why is this view inadequate ''. 



30. What arc the arteries ? Their walls? Their membraae I 



