296 Lieut. -Colonel C. B. Heald and Major W. S. Tucker. 



curve from a case of aortic regurgitation with a high blood pressure, and 

 a very large heart, was taken. It is shown here (fig. 13) as an example of 

 the extreme deflection caused by the hot-wire microphone, when abnormal 

 movements of the body are transmitted to the air in contact with it. 



Conclusion. 



A careful examination of the above records shows that there is an 

 additional periodic effect, besides that of the heart cycle and of breathing. 

 This reveals itself in the variation in heights of the two highest peaks. At 

 certain parts of the record, the first peak is higher, in other parts it is lower 

 than the second peak, while we also get the intermediate conditions of 

 equality of peaks. One of these effects can be partially explained by the 

 difference in sensitivity of the microphone according to the direction of the 

 air current ; but some physiological explanation is required to account for 

 the whole phenomenon, as instrumental variations have been reduced to a 

 minimum. This effect will be the subject of further study. 



The apparatus employed for the recoil measurements is now being further 

 modified, so that the patient can be examined in a recumbent position. 

 Eecords could then be obtained when the muscles are completely relaxed 

 and might easily be taken during sleep. 



This further modification will also permit us to measure the recoil in 

 directions perpendicular to the body axis, so that information regarding the 

 whole of the body movements should then be available. 



Summary. . 



This paper deals with a new method of measuring body recoil as 

 the result of heart action. Attempts have been made to eliminate the dis- 

 turbing factors operating against the success of Yandell Henderson's method. 

 To effect this, the hot-wire microphone with suitable galvanometer and 

 recording apparatus has been employed, and the records actually made 

 measure quantities proportional to the kinetic energy imparted to the body 

 by motions of the blood. In this way slow-moving displacements, such as 

 those of breathing, fail to be recorded. 



The apparatus is of such form that it can be standardised, giving the same 

 responses from day to day for the same body recoils. 



A method is indicated of expressing this kinetic energy of the body in 

 C.Gr.S. units. Attention has been concentrated on the records obtained from 

 a favourable subject, and an analysis of these curves shows that the events 

 of a heart cycle can be recognised. 



