THE CIRCULATION. 171 



agree at what point in the ventricular systole the second 

 sound occurs. In figure 84 are given the views of several 

 of the leading physiologists. It is also an unsettled ques- 

 tion whether the ventricles completely empty themselves, 

 or force out only a certain proportion of the contained blood. 

 Evidence seems to point, however, to the fact that the ven- 

 tricles are practically emptied at each systole. 



Pathological Sounds of the Heart. 



In a normal heart the auriculo-ventricular valves are 

 hermetically closed and permit no blood to flow back. 

 Sometimes, however, these valves become deranged in some 

 way and cease to close perfectly, thus allowing at each con- 

 traction of the ventricle a slight regurgitation of blood into 

 the auricle. The escape of this blood through the imper- 

 fect valves gives a murmuring sound easily detected by the 

 physician by means of a stethoscope, and always an evi- 

 dence that there is a valvular insufficiency. 



THE AMOUNT OF BLOOD FORCED OUT FROM THE HEART. 



It has been difficult to determine exactly the amount of 

 blood forced out from each ventricle at each beat. (It is, 

 of course, unnecessary to point out that the average amount 

 must be the same for both ventricles.) The amount of 

 blood which is found in the ventricles of a corpse is not 

 perfectly reliable, as post mortem changes may have af- 

 fected the size of the heart. The first experiments to de- 

 termine this point gave 175 to 180 grams as the amount 

 sent out by each ventricle at each systole. L,ater experi- 

 ments gave 100 grams, while more recently the amount has 

 been put down as low as fifty grams. Taking 100 grams 

 as probably not far from the truth, it would mean that in 

 one minute (seventy-two beats) 7,200 grams pass through 

 each ventricle, or in one hour 432, 000 grams. This is ap- 

 proximately 900 pounds, or, expressed in fluid measure, about 

 112 gallons. In other words, nor far from three barrels. 

 And as the other ventricle handles a similar amount, it 



