THE CIRCULATION OF THE BLOOD 135 



some fifty thousand of them on the head of a pin. It is 

 said that some five million of them will float round in a 

 single drop of blood. If placed in a row side by side, it 

 would take about thirty-two hundred of them to measure 

 one inch. Under the 



microscope, the sides of , 



these disks stick to one i ^Jlb^ J 



another in rolls, like so 

 many coins. 



FIG. 83. Lateral Section of the 

 Right Chest, showing the Rela- 

 tive Position of the Heart and 

 its Great Vessels, the CEsoph- 

 agus and the Trachea. 



A, a muscle which aids in pushing the 

 food down the oesophagus; , oesoph- 

 agus; C, section of the right bron- 

 chus ; D, two right pulmonary veins ; 

 E, great azygos vein crossing cesoph- 

 agus to empty into the superior 

 vena cava; F, thoracic duct; H, 

 thoracic aorta ; K, lower portion of 

 oesophagus passing through the dia- 

 phragm ; Z,, diaphragm as it appears 

 in sectional view, enveloping the 

 heart ; M, inferior vena cava, pass- 

 ing through diaphragm and empty- 

 ing into right auricle; N, right 

 auricle ; O, section of right branch 

 of the pulmonary artery ; P, aorta ; 

 R, superior vena cava ; S, trachea. 



191. The Work done by the Red Corpuscles. The red 



corpuscles absorb oxygen in the lungs and carry it to the 

 various tissues of the body, which are greedy for it. Night 

 or day, whether we are asleep or awake, millions of these 



