160 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 emo- 

 tions bravery, generosity, mercy, and love. The words cour- 

 age and cordiality are derived from a Latin word signifying 

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

 leai .i by heart, and large-hearted, show how tenaciously these 

 exploded 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 ma- 

 chine, 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 move- 

 ments 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. (Read Note 11.) 



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

 blood away from the heart are the arteries. Their walls are 



11. The Heart. " You all know where it is. It is the most wonder- 

 ful little pump in the world. There is no steam-engine half so clever at 

 its work, or so strong. There it is, in every one of us, beat, beating all 

 day and all night, year after year, never stopping, like a watch ticking ; 

 only it never needs to be wound up, God winds it up once for all." 

 Author of " Rab and His Friends." 



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



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



30. What are the arteries ? Their walls ? Their membrane ? 



