THE ARTERIAL CIRCULATION. 



335 



by one, arid sometimes by two or even three slight undulations, indi- 

 cating a corresponding variation in the tension of the artery during its 

 period of collapse. 



The undulations in the line of descent, in the sphygmograph tracing, 

 are due to an oscillation in the mass of the blood, subsequent to the 

 impulse of the heart, and during the reaction of the arterial system. 

 Marey has shown, by a series of well-conducted experiments, 1 that 

 similar oscillations are produced when any incompressible liquid is 

 driven by a sudden impulse into an elastic tube; and that they are indi- 

 cated by a similar movement of the index of the sphygmograph. When 

 the heart's impulse is moderate, and the tension of the arterial system 

 fully developed, the undulations in the descending line of the pulse are 

 only slightly perceptible ; but when the heart's impulse is more rapid, 

 and the arterial tension diminished, the undulations become more 

 marked. Marey found that he could procure upon his own person 

 traces of different form, in this respect, by simply increasing the tem- 

 perature of the body by the addition of warmer clothing. The following 

 are three traces of the radial pulse obtained in this way, by increasing 

 the quantity of clothing at intervals of twenty minutes. 



Fig. 11 3. 



Fi?. 114. 



Fig. 115. 



VARIATIONS OF THE KADIAL PULSE, under the influence of increased temperature. 



(Marey.) 



Dicrotic Pulse. In certain conditions, accompanied by rapid pulsa- 

 tion of the heart with greatly diminished arterial tension, the rebound 

 or oscillation of the artery becomes so marked, in proportion to the 

 original impulse, that it is easily perceived by the finger, and thus the 

 pulse is apparently reduplicated; that is, there are two pulsations of 

 the artery for each. contraction of the heart, namely, one due to the 

 original impulse, and another due to the oscillation of the blood in the 



1 Physiologic Medicale de la Circulation du Sang. Paris, 1863, p. 266. 



