1885.] of the Heart in Fishes, especially that of the EH. 121 



when the heart recommences after a prolonged standstill, the order of 

 contraction of the different part is, as a rnle, markedly changed, and 

 moreover, the contraction is for the first few beats restricted ( to 

 certain parts of the organ. The remaining parts of the heart remain 

 quiescent for a time, and then come to participate in its activity ; the 

 order of contraction generally remains modified, and it is only after a 

 considerable though variable period that the ordinary succession of 

 events again obtains in the contracting heart. 



The part in which spontaneous contractile activity usually reap- 

 pears after profound inhibition is not the ostial part of the sinus 

 (which ordinarily leads the rhythm of the heart), but the interjugular 

 part of the sinus, which ordinarily contracts second in the series, 

 i.e., in succession to the leading ostial part. The recommencing con- 

 traction is commonly — at least after powerful inhibition — confined for 

 one or more beats to the interjugular parts ; it often extends, how- 

 ever, at the first beat from the interjugular part to the ventricle. 

 The beating of the interjugular part, soon at least accompanied by 

 responsive ventricle beats, goes on for a short though variable time 

 without the slightest movement being perceptible in the auricle or in 

 the ostial part of the sinus. After a time the contraction originating 

 in the interjugular part of the sinus spreads over the ostial part of 

 the sinus, and soon afterwards over the auricle as well as over the 

 ventricle, so that the whole heart is now in actioD, though the order of 

 contraction of its various parts is not identical with that normally 

 present. For instead of the systole being initiated by the ostial beat, 

 it is now initiated by the interjugular beat. Soon, however, the 

 ostial beat regains the precedence and the normal order of events is 

 restored. 



These phenomena seem to depend (1) on the unequal influence 

 exerted by vagal stimulation on the different parts of the heart ; (2) 

 on the high inherent rhythmic power of the interjugular part ; and 

 (3) on the existence of the anatomical and physiological connexion 

 between the sinus and ventricle already mentioned. The ventricle is 

 not directly affected at all by vagus stimulation ; its excitability and 

 contraction force remain quite unimpaired. The interjugular part 

 and the path between it and the ventricle are less profoundly affected 

 than are the auricle and ostial parts ; the former parts recover more 

 readily from the inhibitory influence than do the latter. Early 

 released from inhibitory control, the interjugular part, in virtue of its 

 high rhythmic power, begins to beat, and the contraction is soon 

 propagated to the excitable ventricle. Hence the appearance of the 

 peculiar form of recommencement seen. 



In various fishes besides the eel {e.g., carp) I have observed a 

 somewhat similar mode of recommencing action after inhibition. 

 The sinus and ventricle usually contract once or several times before 



