134 VITAL FUNCTIONS. 



of carbon, or absorbs a quantity of oxygen, as will be seen 

 when we come to treat of respiration. 



399. The two Hearts act together. With respect to the 

 time at which the two hearts act, there is the most won- 

 derful precision and order. The blood which returns from 

 the systematic, and that from the pulmonic circulation, the 

 first through the vena cava, and the other through the 

 pulmonary veins, both fill their respective auricles at the 

 same moment, so that their contractions are simultaneous; 

 and in like manner the ventricles throw their contents, 

 the one to the lungs, and the other to the whole system, 

 at the same instant. So that while the left ventricle is 

 propelling the purified fluid to all parts of the body to 

 renovate its powers, the right ventricle is throwing the 

 vitiated blood to the lungs to prepare it for the same office. 

 Thus the same blood, which during the interval of one 

 pulsation was moving through the lungs, is at the next 

 circulating through the body. 



400. Number of Pulsations, and Muscular Power of 

 the Heart. The ventricle of the human heart contains 

 only about an ounce of blood, but this is changed more 

 than sixty times every minute. Estimating the number 

 of contractions at seventy per minute, which is about the 

 medium number in health, then the quantity of blood which 

 passes through the heart is about three hundred pounds 

 every hour of our lives, making upward of three tuns in 

 each 24 hours. 



401. " An anatomist," says Paley, " who understood the 

 structure of the heart, might say beforehand that it would 

 play ; but he would expect from the delicacy of some 

 of its parts, and the complexity of its mechanism, that 

 it would always be liable to derangement, or that it 

 would soon work itself out, yet does this wonderful 

 machine go on, night and day, for eighty, nay, a hun- 

 dred years together, at the rate of a hundred thousand 

 strokes every 24 hours, having at every stroke a great 

 resistance to overcome, and will continue this action, for 



In what order do the two ventricles of the heart act? What different 

 offices do the two ventricles possess ? How much blood passes through 

 the heart every 24 hours ? 



