I i taal dbs 
ON SPHYGMOGRAPHY. 67 
length of the recording lever, one to its eye, and the other near its 
point, if the tracing be fixed with its lower edge in the same straight 
line as the nail; for then the paper and nail bear the same relation to Page 404. 
one another that the former did to the arbor of the lever when it was 
being recorded. 
Dr. Sanderson,* Mr. Mahomed,+ and others have introduced differ- 
ent ingenious methods for regulating and measuring the pressure 
applied on the artery, which they have described in full in their books 
and papers on the subject; but the desired results can be only approxi- 
mate, as from variations in the elasticity of the skin in different 
individuals and in the same individual under different atmospheric 
conditions, complications are introduced which cannot be eliminated. 
The sphygmograph is a bad hemadynamometer at its best, and as 
such its employment will probably diminish. A glance at the work of 
Dr. Lorainet will show that numberless variations in the character of 
a tracing can be introduced by very small changes in the position, &c., 
of the subject experimented on. But there is one part of the trace 
which is not affected in any way by these complications, and that is 
the relation borne by the length of the different portions of each beat 
to one another. Whether the arm is raised or lowered, whether the 
pressure is great or small, the interval between the systolic rise and 
the commencement of the diastolic rise does not vary in the least. 
These intervals cannot be correctly estimated, except by the aid of the 
sphygmograph; and as the value of any method of investigation is 
greatest in that direction in which it is least influenced by surround- 
ing circumstances, it is, as it will be my endeavour to prove when 
considering the tracings themselves, for the measurement of these 
intervals that we must look for the future value of the sphygmograph. 
Parr II. 
Ty endeavouring to form a correct estimate of the significance of the Page 98. 
various details of the sphygmograph trace, it will be necessary to 
enter somewhat minutely into the consideration of each of the several 
mutually related forces which, by their combined action, produce the 
resulting curve. As some of these forces are but little understood, it 
is clear that any attempt to explain the pulse movements by argu- 
_ ments deduced from tracings obtained from a “ schema” of the circu- 
lation, can only be of value, as far as they relate to forces acting on 
A 
£5 
* Loc. cit. 
+ ‘ Medical Times and Gazette,” 1872. 
t “ Etudes de Médecine Clinique. Le Pouls.” Paris, 1870. 
. F 2 
