292 On the Circulation of the Blood. [Apr. 23, 



measurements of the ratio borne by the cardiosystole * to its component 

 beat in the cardiograph-trace. These tend strongly to substantiate the 

 law previously published by him, viz. that the length of the cardiosystole 

 is constant for any given pulse-rate, and that it varies as the square root 

 of the length of the pulse-beat only being found from the equation 

 #y = 20 V^> where #=the pulse-rate, and 3;= the ratio borne by the car- 

 diosystole to the whole beat. 



A similar series of fresh measurements are given in proof of the law 

 previously published by him, that in the sphygmograph-trace from the 

 radial artery at the wrist the length of the sphygmosystole t is constant 

 for any given pulse-rate, but varies as the cube root of the length of the 

 pulse-beat it being found from the equation xy' = 47 tyx 9 where #=the 

 pulse-rate, and ?/'=the ratio borne by the sphygmosystole to the whole 

 beat. 



By measurement of sphygmograph-tracings from the carotid in the neck 

 and the posterior tibial artery at the ankle, it is then shown that the 

 length of the sphygmosystole in those arteries is exactly the same 

 as in the radial ; so that the above-stated law as to the length of the 

 sphygmosystole in the latter applies to them also, and must therefore 

 apply equally to the pulse in the aorta. 



Such being the case, by comparing the equation for finding the length 

 of the cardiosystole with that for finding the aortic sphygmosystole, the 

 relation between the duration of the whole cardiac systolic act and the 

 time during which the aortic valve remains open can be estimated with 

 facility ; for by subtracting the shorter sphygmosystole from the longer 

 cardiosystole, a remainder is obtained which can. be nothing else than the 

 expression of the time occupied by the ventricle at the commencement of 

 its systole in elevating its internal pressure to that of the blood in the 

 aorta, which must occur before the aortic valve can open up. This in- 

 terval is named the " syspasis" Its length is found to be constant for 

 any given pulse-rate, but to decrease very rapidly with increase in 

 rapidity of the heart's action, becoming nil when that reaches 170 a 

 minute. An attempt is made to explain these phenomena. 



If the above considerations are correct, certain independently obtained 

 measurements ought, on comparison, to correspond ; for by reference to 

 one of the author's papers in the ' Proceedings of the Royal Society/ it is 

 shown that the length of the there-termed second cardio-arterial interval 

 (which may be called the second cardio-radial interval) can only represent 

 the time taken by the second or dicrotic pulse-wave in travelling from 

 the aortic valve to the wrist. This being so, there is every a priori 

 reason in favour of the earlier primary wave taking the same time in going 



* The cardiosystole is the interval between the commencement of the systole and the 

 closure of the aortic valve in each cardiac revolution. 



f The sphygmosystole is the interval between the opening and closing of the aortic 

 valve in each cardiac revolution. 



