490 APPLIED BIOLOGY 



must pump equal amounts of blood, for they beat (contract) 

 together, and each supplies the other with blood. Why then 

 should the walls of the right ventricle be so much thinner than 

 those of the left? The answer is that the right ventricle 

 pumps to the lungs, which are near the heart, while the left 

 ventricle pumps to all the distant parts of the body. It is 

 a familiar fact that a force-pump that empties water into a 

 near-by bucket is easier to work than one connected with a 

 long line of pipe or hose. 



413. Pulse. The well-known throbbing movement of 

 certain arteries (as in wrist and in temple) which are near 

 enough to the skin to be felt with the fingers, is due to a rush 

 of blood through the arteries and a sudden expansion of 

 walls. 



(D) It may be imitated with a soft rubber tube (5 or 6 feet long) 

 connected to a pump or syringe-bulb. While pumping water, 

 steadily pres3 upon the tube with a finger, and note the pulsations 

 which follow each stroke of the pump. Then insert a glass tube with 

 a small opening into the end of the rubber tube, and pump rapidly 

 enough to make the jet of water a steady stream. Now note that 

 the rubber tube is somewhat expanded under internal pressure, and 

 that the "pulse" is still discernible. 



This simple experiment imitates the conditions in arteries. 

 Their walls are elastic, the capillaries exert resistance and 

 prevent the sudden flow of blood through them (just as 

 the small opening at the end of the rubber tube does) ; the 

 blood in the elastic arteries is then under pressure, and 

 the elasticity of the arteries steadily forces blood through 

 the capillaries. 



If the arteries were rigid like glass or iron, there would be 

 no pulse, and blood would be sent in sudden spurts through 

 the capillaries. 



(D) To illustrate this replace rubber tube in experiment above 

 with a tube of glass of same caliber and length. (Any desired length 

 may be made by joining chemical glass tubing with short pieces 



