120 NUTRITIONAL PHYSIOLOGY 



charges blood in like measure. At the conclusion of the 

 active period it may have nearly obliterated its cavity, or 

 the effort may fail while there is still considerable blood 

 within. Estimating an average output from one ventricle 

 to be about 4 ounces, or 100 c.c., it is apparent that forty 

 beats will suffice to discharge from one side of the heart 

 an amount of blood equivalent to the entire quantity of 

 circulation (40 x 100 = 4000 c.c., or 4 liters). In other 

 words, it will require less than one minute for all the blood 

 to pass successively through both sides of the heart. When 

 this statement is made it should be remembered, that 

 certain routes in the systemic circuit are many times longer 

 than others (compare the path to and from the feet with 

 that to and from the esophagus), and some corpuscles may 

 revisit the heart two or three times while others are making 

 one prolonged journey. 



It would be out of place to enter here upon a discussion 

 of the value of the auricles. From a mechanical point of 

 view they contribute but little of the energy required for 

 driving the blood. They serve to accommodate the 

 gathering volume of blood which the veins bring in during 

 the rather prolonged contraction of the ventricles, and they 

 secure a more efficient filling of the lower chambers of the 

 heart. While their muscular development is slight, their 

 automatic power is peculiarly marked, and it is a fair 

 statement that the ventricle, under normal conditions, is 

 stimulated to perform each beat by an influence radiating 

 to it from the auricle. If there is an interruption of certain 

 strands of tissue which normally unite the two, they cease 

 to maintain the same rhythm, the auricle continuing at 

 the accustomed rate, while the ventricle beats much less 

 frequently. When the heart is dying the last signs of 

 pulsation are in the auricles. 



The Portal Circulation. In our general description of 

 the course followed by the blood on its way through the 

 body it was stated that when it has passed through a set 

 of capillaries it is gathered up into veins to be returned 

 to the right auricle. An important departure from this 



