138 VITAL FUNCTIONS. 



a portion of carbon, or absorbs a quantity of oxygen, as 

 will be seen when we come to treat of respiration. 



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 circu- 

 lation, 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 ven- 

 tricle is throwing the vitiated blood to the lungs to pre- 

 pare 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. 



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 70 per minute, which is about the me- 

 dium number in health, then the quantity of blood which 

 passes through the heart is about 300 pounds every hour 

 of our lives, making upwards of three tons in each 24 

 hours. 



" 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 ma- 

 chine go on, night and day, for eighty, nay, an hundred 

 years together, at the rate of an 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 1 What different 

 offices do the two ventricles possess 1 How much blood passes through 

 the heart every 24 hours 7 



