84 PULSE RECORDS IN THEIR RELATION TO 



amongst those who have taken auricular pressure curves, that it 

 occurs earlier (Frey and Krehl, Fredericq, Porter, Hering, and 

 Rautenberg). While it may probably be placed with a fair degree 

 of certainty in the middle or last third of the systolic plateau, 

 there is every possibility that it is subject to variation. The 

 third positive wave ends in the " third negative wave " during 

 ventricular relaxation. Generally the point is given at the bottom 

 of the falling ventricular curve, the instant at which is placed the 

 opening of the auriculo-ventricular valves. 1 Porter himself figures 

 it at a slightly earlier time interval, 2 at a position in the cycle 

 recognised as representing the closure of the semilunar valves, 

 namely, a short distance after the end of the systolic plateau. 



(6) The Venous Pulse in Animals and Mar,. Pulsation 

 of the veins of the neck in pathological conditions is often such 

 an obvious phenomenon that it must have been recognised for 

 many centuries. References to venous pulsation can be traced 

 in the writings of Lancisi ( 30 , p. 182) and Morgagni ( 36 ) in the 

 early and middle years of the eighteenth century. In 1794 

 Hunter described pulsation in the veins of a dog ; but it is ques- 

 tionable if these writers appreciated the extent of the movement ; 

 their observations appear to have been confined to the veins in 

 the immediate neighbourhood of the heart. Later, similar move- 

 ments were described by Weldemeyer (* 8 ) in the veins of a horse. 3 

 Friedreich ( 14 ) took venous curves from the neck of pathological 

 subjects in 1865 ; and two years later Potain ( 40 ) obtained simul- 

 taneous tracings of the apex beat, carotid, radial and jugular 

 pulses in the normal human subject, and his description of the 

 events and his interpretation of them are, in the light of our 

 present knowledge, wonderfully accurate. From the time of 

 Potain's contribution, observations have been published by many 

 writers, amongst whom may be mentioned, Mosso, Gottwalt ( 19 ), 



plateau ; the tracings repeated in Marey's book show the second positive wave, and 

 the third positive wave occurs at the close of systole. The collected curves given 

 by Chauveau in 1887 (Assoc. fraru;. p. I'avanc. d. Sciences) are very various, but 

 as a rule show the three chief waves distinctly. 



1 The point is estimated by differential pressure tracings. 



2 Porter's curves were from the left auricle, and show, like most others, some 

 variation in their last phases. 



3 For full historical accounts the reader is referred to Mackenzie's earlier 

 papers, and the recent publication of Baum (*). 



