THE CIRCULATION OP THE BLOOD. 



221 



ter, the conditions favoring the development of dicrotism are: (1) a 

 highly extensible and elastic arterial wall; (2) a comparatively low mean 

 blood pressure, leaving the extensible reaction free scope to act; (3) a 

 vigorous and rapid stroke of the ventricle, discharging into the aorta a 

 considerable quantity of blood. 



The other secondary waves are probably due to the elastic recoil of 

 the arteries, though some of them at least may be due to the inertia of 

 the instruments used. 



1 234 567 



B 



Fig. 186. A, Normal pulse-tracing from radial of healthy adult, obtained by the sphygmometer. 

 B, From same artery, with the same extra -arterial pressure, taken during acute nasal catarrh. 



In the use of the sphygmograph care must be taken as to the careful 

 regulation of the pressure. If the pressure be too great, the characters 

 of the pulse may be almost entirely obscured, or the artery may be 

 entirely obstructed, and no tracing is obtained; and on the other hand, 

 if the pressure is too slight, a very small part of the characters may be 

 represented on the tracing. 



