THE CIRCULATION OF THE BLOOD 545 



the usual amplitude of the principal secondary 

 vibration is much increased and the interval be- 

 tween the primary and this secondary vibration 

 is not too brief, the pulse may be felt to be 

 double, or " dicrotic." For example, dicrotism 

 can be felt in some cases of continued fever. 



2. A pulse which is felt to reach its maximum 

 slowly is called a " slow pulse " (pulsus tardus). 

 One which reaches its maximum rapidly, giving 

 the palpating ringer the sensation of a quick 

 push, is said to be a " quick pulse " (pulsus celer). 

 Quick and slow pulses should be carefully dis- 

 tinguished from frequent and infrequent pulses. 



Volume. The extent to which the arterial 

 wall is driven from its position of equilibrium 

 (volume or size of pulse) is a function of the 

 output of the ventricle, the outflow period, 

 the peripheral resistance, and the elasticity of 

 the arteries. It is measured very inexactly by 

 the palpating finger and the sphygmograph, accu- 

 rately by the plethysmograph (page 552). 



The Pressure-Pulse in the Artificial Scheme. 

 Kevolve the disk of the artificial scheme until 

 the arterial pressure is maintained at 50 mm. 

 Hg. Close the tube leading to the arterial 

 manometer, so that the oscillations of the 

 mercury may not influence the curves to be 

 taken. Attach the small thistle-tube (without 



