g|8 THE BEASON "WHY. 



"All my bones shall say, Lord, who is like unto thee, which deliverest the poor 



from him that is too strong for him, yea, the poor and the needy 



from him that spoileth him ?" PSALM xxxv. 



vessels do not sustain themselves upon the blood, which they contain 

 but receive into their coats numerous capillary vessels by which 

 they are nourished. 



920. Sow much Hood does the human body contain ? 

 From twenty-five to thirty-five pounds. (See 623.) 



921. Soio does the Hood ascend in the veins, in opposition 

 to gravitation ? 



In addition to the muscular coats of the veins, and the influence 

 of muscular action upon them, there are in the veins numerous 

 semi-circular valves, which are not found in the arteries. These 

 valves extend from the sides of the veins in such a manner that they 

 allow the free passage of the blood upwards, but a backward motion 

 of the blood would expand the cup-like valves and stop the passage ; 

 BO that the blood can only move in one direction, and that towards 

 the heart. 



922. Sow frequently does the total amount of blood circu- 

 late through the system ? 



The blood circulates once through the body in about two minutes. 

 If, therefore, we estimate the amount of blood at twenty-four pounds, 

 it follows that no less than twelve pounds of blood pass through the 

 heart every minute ; and it is estimated that if the blood moved with 

 equal force in a straight line it would pass through one hundred and 

 fifty feet in a minute. 



CHAPTEE XLV. 



923. Sow many bones are there in the human body f 

 There are two hundred and forty-six, and they are apportioned 

 to the various parts of the body in the following numbers : 



Head 8 



Ears 6 



Face 14 



Teeth 32 



Back-bone and its base ... 26 

 Chest, &e. . 26 



