Page 99, 
68 ON SPHYGMOGRAPHY. 
the “schema” which are strictly comparable with similar forces at 
work in the human body. This consideration has prevented my 
basing any deductions on facts derived otherwise than from the 
animal body itself. 
To commence with, it will be necessary to describe the tracings 
obtained by means of the “ Hemadromograph” of Chauveau. Dr. 
Lortet, of Lyons, has given an excellent figure and description of this 
instrument,* which, from its simplicity and efficiency, is a perfect 
masterpiece of mechanical design. By means of two levers it indicates 
on a revolving drum both the modification in the diameter of an 
artery during a pulse-beat, and also the changes in the velocity of the 
blood-current at the same spot, simultaneously. The former of these 
results is obtained by the use of an ordinary sphygmoscope, an instru- 
ment which measures indirectly the modifications in the area of an 
artery ; and the latter by a long lever which, at its attached end, after 
passing through a slit in the side of the tube, projects a short dis- 
tance into the vessel, which allows of its being moved backwards and 
forwards by the blood-current. 
The accompanying trace (Fig. 1), taken with this instrument from 
the carotid of the horse, is copied from Dr. Marey’s work.t 
Fig. 1. Hemadromograph trace from the carotid of the horse. 
a, The current trace, in which the horizontal dotted line is the zero, indicating 
no current in either direction. 
B. The sphygmoscope trace. 
In both, the vertical line 1 cuts the curve at the commencement of systole, the 
line 3 at the moment of closure of the aortic valve, and the line 4 when the centri- 
fugal current recommences. 
The figure reads from left to-right. 
* ** Recherches sur la Vitesse du Cours du Sang dans les Artéres du Cheval.” 
Par M. L. Lortet, M.D. ‘ Annales des Sciences Nat.,” Tome VII. Zoologie, 1867. 
An earlier but very similar instrument, by M. Chauveau, is described in Marey’s 
“ Physiologie Médicale de la Circulation du Sang,” 1868, p. 156. 
+ Loc. cit., p. 273. 
