320 Mr. A. H. Garrod on the relation of the Cardiograph [Feb. 23, 



and as they are both recorded on the same paper, synchronous movements 

 must be at equal distances from the starting-points, and therefore they can 

 be projected on one another. The results obtained by these projections 

 form the subject of this communication. 



All the observations were made on the same subject, setat. 24, in good 

 health. They were all made in the sitting posture, as the apparatus could 

 then be held more firmly, or rested on the arm of a chair. 



To facilitate description, the following terms and symbols will be em- 

 ployed with regard to pulse-traces. 



1. The rapidity of the pulse is symbolically represented by x. 



2. The first cardiac interval is that which occurs between the commence- 

 ment of the systolic rise and the point of closure of the aortic valve, in 

 cardiograph traces. The number of times that this interval is contained 

 in its component beat is represented by y ; and the law as to its length, 

 published elsewhere*, will be assumed; it may be stated thus : 



xy=20V x. 



3. The first arterial interval is that which occurs between the com- 

 mencement of the primary rise and the termination of the major fall in 

 arterial sphygmograph traces. The number of times that this interval is 

 contained in its component beat is represented by y'; and the law as to its 

 length at the radial artery, which is alone considered in this communica- 

 tion, published in the Proceedings of the Royal Society (No. 120, 1870), 

 will be assumed ; it may be thus stated : 



" xy^=A7^/x. 



4. The first cardio-arterial interval is that which occurs between the 

 commencement of the systolic rise in the cardiograph trace and the origin 

 of the main rise in the sphygmograph trace. The number of times that 

 this interval is contained in its component beat is represented by z. 



5. The conjugate cardio-arterial interval is that portion of the first 

 cardiac interval which is synchronous with a portion of the first arterial 

 interval. It is therefore the interval between the commencing sphyg- 

 mograph rise and the point of closure of the aortic valve as represented in 

 the cardiograph trace. 



6. The second cardio-arterial interval is that which occurs between the 

 point of closure of the aortic valve and its indication at the artery under 

 consideration. . 



In commencing to work with the cardio-sphygmograph, measurements 

 were made to find the duration of the first cardio-arterial interval, as it 

 required but a few experiments to prove that the heart commences to 

 contract before the pulse is indicated at the wrist. 



By means of compasses, or by superposing one trace on the other, the 

 commencing cardiograph rise was projected on the sphygmograph trace ; 

 and the interval between this event and the origin of the radial rise was 

 * Journal of Anatomy and Physiology. Cambridge, vol. v. Nov. 1870. 



