1921] The Law of the Heart 



WEEKLY EVENING MEETING, 

 Friday, May 20, 1921. 



Sir James Reid, Bart., G.C.Y.O. K.O.B. M.D. LL.D. P.R.O.P., 



Manager and Vice-President, in the Chair. 



Professor E. H. Starling, C.M.G. M.D. D.Sc. 

 F.R.C.P. F.R.S. 



The Law of the Heart. 



The discovery by Harvey of the circulation of the blood, and of 

 the part played by the heart in carrying on this circulation, is one 

 of the few scientific discoveries which have become common know- 

 ledge. We have to think of the body as a collection of mechanisms 

 or machines, each one of which is doing some form of work for one 

 common end — i.e. the preservation of the body. For this work the 

 oxidation of the food taken in at intervals during the day provides 

 the energy ; thus each part of the body must be supplied not only 

 with food derived from the alimentary canal, but also with the oxygen 

 taken in with the air we breathe into the lungs. Like any other 

 machine, each body mechanism produces, as a result of this consump- 

 tion of the food, w T aste gases and other waste products which have to 

 be carried to the lungs or to the kidneys and there cleared out of the 

 body. It is for this reason that the existence of the higher animal 

 demands a common fluid, the blood, which can carry food, oxygen or 

 carbonic acid, and which is maintained in continual circulation 

 between all the organs of the body, so that the alimentary canal, for 

 instance, may serve for the maintenance of all parts, and the lungs 

 can supply oxygen to these parts or excrete the carbonic acid which is 

 produced as a result of their activity. 



But a uniform mechanical circulation would be of little value to 

 the body, since the activities of all its parts vary within wide limits. 

 Thus, during muscular exercise the activity of the muscles may be 

 increased ten-fold or more, and this increase means a corresponding 

 augmentation in their call for oxygen and in the quantity of waste 

 products, especially carbonic acid, that they produce. Since the 

 oxygen is carried by the blood, it follows that for the continued 

 functioning of the muscles these must receive a blood supply which 

 is ten times greater during activity than during rest, if their activity 

 is not to be brought to an end by a species of suffocation. We thus 



