CHAPTER III. 



THE HEART. 



The blood in the body has to be kept in constant motion 

 in order that the tissues which are depending upon it for 

 their vitality may be continuously supplied, and also in order 

 that the impure fluid resulting from these changes, may be 

 rapidly and effectually conveyed to those organs where its 

 purification is carried, out. 



The heart is the organ which pumps the blood over the 

 body, not only distributing it to the tissues, but forcing 

 it on from these back to the heart again to be prepared for 

 redistribution. It may be described as a hollow muscle 

 divided into two compartments, right and left, each com- 

 partment being capable of division into an upper one or 

 auricle, and a lower or ventricle. Opening into the auricles 

 are large veins which convey the blood back from the body 

 for redistribution by the ventricles ; the two cavities are 

 separated by a valvular arrangement. From the ventricles 

 other vessels, arteries, take their origin for the conveyance 

 of blood from the heart. 



So far the general arrangement of both right and left 

 sides of the heart are much the same, each having to 

 receive and then to get rid of a certain quantity of blood 

 pumped into it ; but the blood pumped into the right heart 

 is very different from that pumped into the left, and it is 

 with these differences that we must for a moment deal. 



Into the right heart the whole of the impure or 

 venous blood in the body is brought, for the purpose of 

 being purified in the lungs : into the left heart the 



