PURE AIR 



107 



bodies are equipped in a similar way ? This is exactly 

 the case. Situated in the chest between the lungs, 

 and a little below the neck, is a thick muscular organ 

 called the heart. We can tell by the illustration that 

 it is shaped like a pear, and has its small end turned 

 downward and .a little to the left. If we were to 

 dissect a sheep's heart, which 

 is formed like our own, we 

 should find that it has two 

 distinct sides, and that each 

 side has two separate 

 chambers. The chambers on 

 the right side are named 

 right auricle and right ventri- 

 cle, while those on the left 

 side are the left auricle and 

 left ventricle. 



If we could see the workings 

 of the heart, we should observe 

 that dark, impure blood 



pours through two large veins, which come one from 

 above and one from below and lead into the right auri- 

 cle. As soon as this chamber is full, the contraction 

 of the muscles forces the blood it contains into the 

 right ventricle. This, contracting in turn, drives it 

 through the pulmonary artery and its many branches 

 into the countless blood-vessels that spread all through 

 the membrane of the five or six million air-cells of the 

 lungs. On its journey through these capillaries the 



The Heart. 



