ON SPHYGMOGRAPHY. 63 
10. ON SPHYGMOGRAPHY.* Page 399. 
Part L 
Ir is to the happy conception of Marey’s, in which he obtained correct 
amplification of sudden small movements by employing the elastic 
force of a spring rather than the statical pressure of weights, that we 
owe the form of Sphymography, now well known to most students of ; 
physiology ; and the introduction of this fresh method of research has 
given a stimulus to the progress of precise thought respecting the cir- 
culation of the blood and the action ©f the heart, which must neces- 
sarily prove of extreme value in the investigation of pathological 
conditions, now quite beyond our grasp. 
Marey’s original instrument, as constructed by Breguet, is so well 
known, and so many excellent descriptions are accessible,t that it is 
not necessary to go into detail regarding it. In most respects it is 
the best form that has been introduced, and much credit is due to 
M. Breguet for the excellence of the mechanical construction. This 
maker has lately introduced a second instrument, which has the advan- 
tage of removing the chief defects of the original one, and of intro- 
ducing very little intrinsic error. 
The chief objection to the old, or knife-edge construction, as it 
may be called, from the fact that the recording lever is connected with 
the pulse pad by means of a sharp steel edge, depends on the necessary 
sliding of that knife-edge on the steel surface below the recording 
lever, by which means the distance between the axis of rotation of the 
lever and the point of contact of the knife-edge must vary with every 
movement of the former; the accompanying diagram shows how this is 
the case for two different heights of the lever. 
In consequence of this imperfection, two traces taken, one near the 
top, and the other lower down on the recording paper, present cha- Page 400. 
racteristics which are in many respects different, and whose differences 
arise solely from the sliding above mentioned. The lever in the upper 
trace falls less rapidly than in the lower, as the knife-edge has to slide 
over a much larger surface in the former than in the latter, where it 
scarcely moves at all. Asa result of this, the length of the first part 
of the higher trace is apparently greater than it ought to be. 
* Part I, “ Journal of Anatomy and Physiology,” VI. pp. 399-404. May, 1872. 
Part IT, lc. VII. pp. 98-105. Nov. 1872. 
+ Marey, “Physiologie médicale de la Circulation du Sang,” Paris, 1863; B. F. 
Foster, M.D., ‘‘ On the use of the Sphygmograph in the Investigation of Disease,” 
1866; J. Burdon Sanderson, M.D., F.R.S., “ Handbook of the Sphygmograph,” 
1867 ; and others. 
