WORK DONE BY THE HEART. 311 



that different parts of the column of fluid move with different 

 velocities. Down the centre of the stream the red corpuscles are 

 seen coursing rapidly, while between the central part and the 

 vessel wall on each side a pale line of plasma can be recognized, 

 which seems to flow more slowly and to carry with it only a few 

 white corpuscles. 



In the veins the velocity varies enormously with a variety of 

 circumstances which have little or no effect on the arterial flow. 

 Thus, the position of the body or limb, the activity of the neigh- 

 boring muscles and the respiratory movements alter it, but as a 

 general rule the flow in the veins is pretty steady, there being no 

 pulsation or corresponding variation of velocity. In the large 

 vessels the onward flow is affected by the contraction of the auri- 

 cles. During the auricular systole the- veins cannot empty them- 

 selves, and therefore there is a slight check to the onward flow, 

 and the velocity of the current is accordingly reduced. In cases 

 where the auricles are dilated and distended with blood this may 

 cause a definite pulsation, which becomes visible in the great veins 

 of the neck. 



WORK DONE BY THE HEART. 



This can only be determined when the mechanism of the ves- 

 sels is understood. The amount of work done by any form of 

 engine may be expressed as so many kilogrammetres per hour. 

 That is to say, the numbers of kilogrammes it could raise to the 

 height of one metre in that time. 



The left ventricle moves with each systole about 0.188 kilo- 

 gramme of fluid against an arterial pressure corresponding to 

 3.20 metres height of blood, i.e., 0.188 X 3.21 = 0.604 kilogram- 

 metres for each systole. This at 75 per minute for twenty- four 

 hours would be 



0.604 x 75 x 60 x 24 = 65,230 kilogrammetres. 



The right ventricle does about one-third as much work as the 

 left, making a total of 86,970 kilogrammetres for the ventricles, 

 or, in other words, the heart of a man weighing twelve stone does 



