EXPLANATION OF Sl'IlYGMOGKAPHIC TKACINGS. 103 



produces, and the long and rounded apex of aortic obstruction. 

 There is, liowever, a marked difference between the tracings 

 from the two radials, the ascent of the wave being more abrupt, 

 tlie top flatter, and the descent distinctly dichrotic in the right, 

 while in the left the ascent is less abrupt, as shown by the 

 smaller hook at the top ; the maximum height is not attained 

 til] near the end of the systole, and there is generally little or 

 no dichrotism in the descent. This might be due to aneurism ; 

 but there were no physical signs to show its presence, and in 

 the absence of a post-mortem examination, or experiment with a 

 schema, hypotheses as to the cause of difference are of little 

 value. 



The tracings taken during an attack were chiefly from the 

 right radial. The only one I got while the pain was actually 

 coming on is unfortunately an imperfect one (No. 1, May 28th, 

 Fig. 121). From this tracing, and from those taken when the 

 pain was becoming worse (Xos. 1 and 2 of May 17th, Figs. 117 

 and 118), it will be seen that as the pain increased the curve 

 became lower, bcth the ascent and descent more gradual, and 

 the dichrotism disappeared. This form of curve clearly indicates, 

 that the arterial tension is much increased, and this increase can^ 

 I think, be due only to contraction of the small systemic vessels, 

 so sudden and so great as well to deserve the name of spasmodic. 

 As I have stated in a former paper,* this increased tension led me 

 to suggest nitrite of amyl to relieve the spasm.-f* The rapidity 

 with which this increase in tension takes place is shown by the 

 great change which the form of the pulse has undergone in 

 Tracing 1, May 28th, during the short time occupied in re-ink- 

 ing the pen. It would seem from Tracings 3 and 4 (Figs. 115 

 and IIG) of the plate tliat the tension in the right radial was 

 raised more than in the left, and farther experiments w4th 

 simultaneous tracings are necessary to decide whether the spasm 

 extends to all systemic vessels or to all alike. 



At the same time that the tension increases the pulso be- 

 comes somewhat quicker, which shows that there is some dis- 



* Lancet, July 27tli, ISO", cf. dntea, p. 137. 



t Dr. Ecnnett, on being informed of the successful result of tlie first experi- 

 ment, ordered the inhalation to be continued. 







