234 THE HUMAN BODY. 



kilogrammeters (325,584 foot-pounds). The pressure in the 

 pulmonary artery against which the right ventricle works is 

 about ^ of that in the aorta; hence this ventricle in twenty- 

 four hours will do one third as much work as the left, or 

 15,120 kilogrammeters (108,528 foot-pounds), and adding 

 this to the amount done by the left, we get as the total work 

 of the ventricles in a day the immense amount of 60,480 

 kilogrammeters (434,112 foot-pounds). If a man weighing 

 75 kilograms (165 Ibs.) climbed up a mountain 806 meters 

 (2644 feet) high his skeletal muscles would probably be 

 greatly fatigued at the end of the ascent, and yet in lifting 

 his Body that height they would only have performed the 

 amount of work that the ventricles of the heart do daily 

 without fatigue. 



The Plow of the Blood Outside the Heart. The_blood 

 leaves the heart intermittently and not in a regular stream, 

 a quantity being forced out at each systole of the ventricles: 

 before it reaches the capillaries, however, this rhythmic 

 movement is transformed into a steady flow, as may readily 

 be seen by examining under the microscope thin transparent 

 parts of various animals, as the w r eb of a frog's foot, a mouse's 

 ear, or the tail of a small fish. In consequence of the steadi- 

 ness with which the capillaries supply the veins the flow in 

 these is also unaffected, directly, by each beat of the heart; 

 if a vein be cut the blood wells out uniformly, while a cut 

 artery spurts out not only with much greater force, but in jets 

 which are much more powerful at regular intervals corre- 

 sponding witfi the systoles of the ventricles. 



The Circulation of the Blood as Seen in the Prog's Web, 

 There is no more fascinating or instructive phenomenon than 

 the circulation of the blood as seen with the microscope in 

 the thin membrane between the toes of a frog's hind lirnb. 

 Upon focusing beneath the epidermis a network of minute 

 arteries, veins, and capillaries, with the blood flowing through 

 them, comes into view (Fig. 91). The arteries, a, are 

 readily recognized by the fact that the flow in them is fastest 

 and from larger to smaller branches. The latter are seen 

 ending in capillaries, which form networks, the channels of 

 which are all nearly equal in size. While in the veins aris- 

 ing from the capillaries the flow is from smaller to larger 

 trunks, and slower than in the arteries, but faster than in the 

 capillaries. 



