176 THE CIRCULATION 



is capable of a distinct chemical reaction (as potassium ferro- 

 cyanide, or barium nitrate) be introduced into a vein on one 

 side of a horse, and at the end of twenty or thirty-two seconds 

 blood be taken from a distant vein on the other side, its 

 presence may be detected. In man, the blood moves with 

 greater speed, and the circuit is completed in twenty-four 

 seconds. 



47. What length of time is required for all the blood of the 

 body to make a complete round of the circulation? This 

 question cannot be answered with absolute accuracy, since the 

 amount of the blood is subject to continual variations. But, 

 if we assume this to be one-eighth of the weight of the body 

 about eighteen pounds it will be sufficiently correct for our 

 purpose. Now to complete the circuit, this blood must pass 

 once through the left ventricle, the capacity of which is two 

 ounces. Accordingly, we find that, under ordinary circum- 

 stances, all the blood makes one complete rotation every two 

 minutes passing successively through the heart, the capil- 

 laries of the lungs, the arteries, the capillaries ef the extremi- 

 ties, and through the veins. 



48. That portion of the blood which passes through the 

 spleen, pancreas, stomach, and intestines differs from the rest 

 of the blood in that it has to pass through the liver. This is 

 known as the portal division, while that passing through the 

 lungs is the pulmonary division, and that through the rest of 

 the body the systemic division. All the blood coming from 

 the organs above enumerated is collected by the veins,, which 

 unite to form what is called the portal vein. From here the 

 blood, filled with all the products of digestion, passes through 

 the cells of the liver, where all the glucose is abstracted from 

 the blood and stored up as glycogen. The blood is then col- 

 lected in a second set of capillaries, which go to form the 

 hepatic vein; and this in turn conveys the blood to the 

 inferior vena cava, and so on to the right auricle. The liver 

 itself is nourished by fresh arterial blood through the hepatic 



47. Time required for all the blood in the body to circulate completely around ? 



48. What can you say of the blood which passes through the li ver ? 



