S QtJAtEROENTfiNAkV StUDtES ik PAtHOLOGV 



small. This condition, however, leads to a rhythmical variation in the 

 strength of the pulse, as has been shown by one of us in the case of 

 certain poisons which lead to a ventricular rhythm independent of and 

 different from that of the auricle.* No such rhythmical variation in the 

 size of the pulse is to be made out in this case, so that the condition is 

 obviously different from that occurring in animals under these poisons. 

 An irregular and intermittent beat of the auricle might, however, cause 

 the occasional discharge of blood into the ventricle during the diastole, 

 and thus lead to a large pulse wave from the next ventricular contrac- 

 tion ; the ventricular rhythm must then be much more rapid than 

 that of the auricle, and, of course, must be developed indepen- 

 dently. Another factor which may determine the variations in the 

 strength of the pulse in this case is imperfect diastole of the ventricle. 

 The blood can flow from the auricle only when the intra-auricular 

 pressure is higher than the intra-ventricular, and, if the ventricle remains 

 half-contracted during the diastole, the inflow must be small and the 

 next pulse correspondingly low. If this be the correct explanation of 

 the variations in the size of the pulse, these are, of course, due to the 

 ventricle alone. The auricle might be beating at the same rate as the 

 ventricle, but unable to empty itself against the half-contracted ventricle, 

 or it might be entirely inactive, the blood simply entering the ventricle 

 from the auricle through the pressure exerted on it by the right heart. 



Which of these two factors determines the variations in the size of 

 the pulse we are unable to determine from the evidence of the tracings. 

 If the venous pulse had been registered simultaneously with the arterial, 

 much light would have been thrown on the point, and it would probably 

 have been possible to decide whether slow, intermittent, irregular con- 

 tractions of the auricle are the explanation, or variations in the degree of 

 relaxation of the ventricle. In the absence of such evidence, the latter 

 appears the preferable. It is a feature familiar to everyone who has 

 watched an irregular heart in the living animal, while it is extremely 

 rare to find the auricle beating so much more slowly than the ventricle 

 as would be indicated by the number of full pulses. 



The regular beat of the ventricle which is registered by the sphygmo- 

 graph in normal persons follows an impulse which originates in the 

 " rhythmic area " around the great veins of the heart, and is propagated 



* Journal of Physiology^ xxv., p. 49. 



(102) 



