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Recoil Curves as Shoivn by the Hot- Wire Microphone. 



By Lieut.-Colonel C. B. Heald, C.B.E., M.D., and Major W. S. Tucker, 



R.E., D.So. 



(Communicated by Prof. C. S. Sherrington, P.R.S. Received November 15, 1921.) 



[Plates 5-8.] 



Introductory Eeviarks. 



The subject matter of this paper deals largely with a description of a 

 process which, in its bearing, appertains to physics rather than physiology, 

 but as the application is entirely physiological, it has been decided to submit 

 it as a physiological contribution. 



In 1916, one of us (W. S. T.), while at work on the perfection of the hot- 

 wire microphone, which he had invented for the location of enemy guns, 

 realised the possibilities of the hot-wire microphone for obtaining records of 

 the pulse, apex beat, etc., and had actually taken records both from the wrist 

 and neck, and had shown these to members of the medical profession. 



In the same year, when one of us (C. B. H.) was working upon the 

 examination of cadets for pilots' certificates in the Royal Flying Corps, a 

 converted " penny-in-the-slot " weighing machine was used for recording the 

 weight. It was noticed that the machine would not permit an absolutely 

 steady reading to be taken, as the point of the hand was in constant move- 

 ment. Closer observation of this movement showed that it took place in time 

 with the heart beat. 



The obvious explanation of the movement of the hand was that the 

 propulsion of the blood from the left ventricle of the heart towards the head 

 during the first stage of systole was accompanied by a corresponding opposite 

 movement of the body towards the feet. If this assumption were correct, 

 then, knowing the weight of the body, measurement of the actual distance 

 through which it was moved would provide a useful factor in determining the 

 efficiency of the heart when regarded as a mechanical pump. 



This simple observation with the weighing machine sufficed, however, to 

 attract attention to the importance of employing the recoil of the body for 

 the measurement of heart efficiency, the heart being considered as a pump. 



The only previous work along these lines appears to be that undertaken by 

 Prof. Yandell Henderson (7), who used a swinging table, in which lateral 

 movements were prevented by an ingenious device ; he was thus able to 



vol. xciii. — b. x 



