SOME PHYSIOLOGY YOU OUGHT TO KNOW 3 1 



farther away further subdivides until there is a 

 great network of little arteries; these in turn be- 

 come very tiny and take the name of capillaries. 

 Thus the red blood, by means of arteries and capil- 

 laries, is carried to all parts of the body. This 

 plan of distribution would not be complete unless 

 some way were provided for the return of the blood 

 to the heart and lungs for purification. And just 

 such an arrangement has been provided. Another 

 kind of network collects this scattered blood at the 

 extremities into separate vessels, which gradually 

 increase in size and finally empty their possessions 

 into the heart. These are the veins of the body, 

 and have to do with the impure blood of the body. 



How the Heart Does Its Work. — The power back 

 of blood distribution is the heart. It is an auto- 

 matic pump, as it were, that sends blood to the 

 lungs and through the arteries to all parts of the 

 body. The heart is divided into four divisions : 

 the left and right ventricles and the right and left 

 auricles. The right auricle receives the blood from 

 the upper half of the body through a large vein 

 and the lower half of the body through another 

 large vein, and the blood from both lungs empties 

 into the left auricle through two left and two right 

 pulmonary veins. The large arteries of the heart 

 which carry the blood from the heart to the dif- 

 ferent organs arise from the ventricle. 



The blood always flows in the same direction. It 

 goes into the auricle from the veins, and from this 

 into the ventricle. It then passes into the arteries, 

 then to the veins and then to the capillaries. 



The action of the heart is very much like a force 

 pump; the dark blood flows into the right auricle, 

 which contracts; when this is done, the blood is 



