1870.] Mr. A. H. Garrod on the Sphygmograph Trace. 351 



The values of Q are strictly equivalent to each other in point of activity. 

 The author believes that a is commensurate with the elective function of 

 chemical attraction, first discovered by Bergman. He terminates the 

 memoir with a reference to some well-known instances of chemical action 

 (such as that of argentic nitrate on a mixture of aqueous potassic chloride, 

 bromide, and iodide), as serving to bestow a presumptive generality on his 

 principal conclusions. 



V. "On the relative Duration of the Component Parts of the Radial 

 Sphygmograph Trace in Health." By A. H. Garrod, of 

 St. John's College, Cambridge. Communicated by Dr. Gar- 

 rod. Received April 23, 1870. 



The graphic method of representing the various phenomena occurring in 

 the body during life, which has been so much developed by MM. Marey 

 and Chauveau of Paris, has placed within our reach great facilities for 

 obtaining an accurate knowledge of the relations, in point of time, of 

 mutually dependent physiological events, and the sphygmograph has be- 

 come, among others, an instrument familiar to most interested in science. 



By means of this instrument, a detailed and truthful record can be 

 easily obtained of the modifications in the diameter of any superficial 

 artery, and, as usually constructed, it is intended to be applied to the 

 radial at the wrist. 



The traces to be referred to were taken with one of Marey's instru- 

 ments, as made by Breguet. The recording paper ran its whole length, 

 4-f inches, in seven seconds, and thus, by counting the number of pulse- 

 beats in each trace, and multiplying the number thus obtained by 8*57143, 

 the rate of the pulse at the time the trace was taken was easily found. 



The lever-pen was of thin steel, sharply pointed, and it recorded by 

 scratching on highly-polished paper previously smoked. 



It is now generally agreed that in each pulsation of the radial sphygmo- 

 graph trace, the main rise is the effect of the contracting ventricle send- 

 ing blood into, and thus filling, the arterial system. 



This rise is followed by a continuous fall when the pulse is quick, but 

 when slow, its continuity is interrupted by a slight undulation, convex 

 upwards. 



The major fall is followed by a secondary rise, not so considerable as 

 the main one, but more marked than any other, and this secondary rise is 

 evidently due to the closure of the aortic valves preventing further flow of 

 blood heartwards. 



The two points therefore, the commencement of the primary and of the 

 secondary rise, may be considered to mark the beginning of the systole of 

 the heart, and the closure of the aortic valve respectively, as far as they 

 influence the artery at the wrist ; and the interval between these two 

 events may be called the first part of the arterial sphygmograph trace, 



