VASOMOTOR NERVES. 317 



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 kilogram metres 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 3.20 = 0.604 kilo- 

 grammetres 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 

 as much work in twenty-four hours as would be required to lift 

 his body 1248 yards into the air,i. e., nearly ten times as high as 

 the top of St. Paul's Cathedral. 



CONTROLLING MECHANISMS OP THE BLOOD VESSELS. 

 Vasomotor Nerves. 



That the arteries possessed, as well as elastic resiliency, vital 

 contractility, which regulated the amount of blood flowing to any 

 given part, was well known to John Hunter. 



The muscle cells have also been long since clearly demonstrated 

 in the middle coats of the arteries, but nothing was known of the 

 nervous channels which bore the stimulus to the vessels, or the 

 nerve centres which regulated their contraction, until compara- 

 tively recent times. 



The first knowledge concerning special nervous arrangements 

 for the control of the muscular wall of the vessel was given to 

 us by Claude Bernard, in his notable experiment of cutting the 

 sympathetic nerve in the neck, which was always followed by an 

 increase in temperature of that side of the head, and a great 

 expansion and overfilling of the arteries. 



It was further observed that stimulation of the superior gan- 



