ON SPHYGMOGRAPHY. 69 
The upper curve («) is that of the blood-current; in it the horizontal 
‘dotted line indicates the zero, or line of no current in either direction; 
all above shows a centrifugal current, and all below a heartward 
stream. The velocity of the blood’s movement is measured by the 
distance of the point which is under consideration from the zero line 
in the trace. The lower curve is that obtained by the sphygmoscope, 
and is in all respects strictly comparable with an ordinary sphygmo- 
graph tracing. The slightly curved vertical lines which intersect 
both tracings are drawn by the levers when the watchwork is at rest, 
and the points where similarly situated lines intersect the pulse traces 
are exactly simultaneous, to indicate which they are drawn. With 
regard to these figures, Marey makes the following observations :— 
“I. The commencement of the pulsation coincides with the produc- 
tion of a rapid centrifugal current. II. The summit of the pulsation 
is not reached before the centrifugal current has already ceased. 
Ill. At the instant of closure of the sigmoid valves, a retrograde 
current is flowing in the carotid, as indicated by the position of the 
curve, which at that moment is below zero. IV. After the closure of 
the sigmoid valves a fresh centrifugal current originates, which consti- 
tutes the secondary pulsation—(dicrotism).” Dr. Lortet explains the 
portion of the upper or current-trace which is below the zero line, by Page 100. 
_ supposing that the shock of closure of the sigmoid valves is sufficiently 
“great to produce a stretching of the proximal end of the aorta and of 
; the valves themselves, which results in a retrograde current for a short 
time in the large arteries after the valves have closed. Marey’s expla- 
nation, as far as it goes, seems much more satisfactory, and it will be 
necessary to discuss it more fully. Before doing so the precise defini- 
tion of some of the terms employed will not be out of place. The main 
rise in the sphygmograph trace may be termed the primary rise, and 
that which occurs just after the small rise and fall which is nearly 
simultaneous with the sinking of the current-trace below the zero, and 
which therefore commences with the secondary centrifugal current, 
may be termed the secondary rise; it is almost always very clearly 
indicated in sphygmograph tracings (c, a, Fig. 2). The interval be- 
tween these two rises may be called the sphygmosystole, for it is the 
ie time during which the systole at the heart influences the pulse-beat; Page 101. 
it corresponds to the first part of the pulse-beat in my former com- 
munications, and it must be remembered that it is not synchronous 
with the cardiac systole, as 1 have endeavoured to show elsewhere.* 
From a study of tracings obtained by the use of the cardio-sphyg- 
mograph I have demonstrated, in the paper just referred to, that in 
2 
7 
* “ Proceedings of the Royal Society,” 1871, p. 318, e¢ seg. (Supra, p. 32), and 
“ Journal of Anatomy and Physiology,” May,1871. (Supra, p. 27.) 
