528 CIRCULATION OF BLOOD AND LYMPH. 



ventricular bundle, which constitutes the physiological link con- 

 necting the auricles and ventricles.* 



In the hearts of the cold-blooded animals the same general 

 results are readily obtained when the tissue between the different 

 chambers is compressed or destroyed. In the frog's heart, for 

 instance, if one ties a ligature (first ligature of Stannius) between 

 the sinus venosus and the auricle, the auricle and ventricle cease 

 beating while the sinus continues pulsating with its normal rhythm. 

 Later the auricle and ventricle may commence beating again, but 

 if this happens their rhythm is slower than that of the sinus and 

 independent of it. So in the terrapin's heart, in which the sequence 

 of beat is so beautifully exhibited, if one ties a ligature between 

 auricle and ventricle, or cuts off the ventricle entirely, the sinus 

 venosus and auricle continue beating at their normal rhythm, while 



1 2 



Fig. 217. Cardiogram from a case of Stokes-Adams disease, showing two auricular beats 

 (1, 2) to each ventricular beat. (Erlanger.) The time-record marks fifths of a second. 



the ventricle remains usually entirely quiescent so long as normal 

 blood flows through it. It would seem from these facts that in the 

 mammalian heart the ventricle when disconnected from the auricle 

 is capable of maintaining a fairly rapid rhythm of its own. At the 

 other extreme, the terrapin's ventricle when similarly treated shows 

 no spontaneous beats at all. These and many other facts that 

 might be quoted support well the general view proposed by Gaskell, 

 that the venous end of the heart possesses the greater rhythmical 

 power and starts the heart beat, and that the wave of contraction 

 is propagated from chamber to chamber through the intervening 

 muscular substance. 



There remains a deeper question as to what occasions this greater rhyth- 

 micity at the venous end, a question that is, of course, bound up with the 

 problem of the ultimate cause or conditions of automatic rhythmicity. In 

 connection with this latter problem the absolute necessity of the presence of 

 certain inorganic salts in certain proportions has been emphasized. In this 

 same general line the author has called attention to the fact that in the ter- 

 rapin the amount of potassium salts present in the blood explains in itself 

 why the sinus sets the heart rate. In blood, or in Ringer's solution con- 

 taining potassium salts in the same amounts as blood, the ventricular muscle 

 is not automatically contractile; the sinus end of the heart, on the contrary, 

 beats well in such media, while an increase in the potassium contents will 



* See Erlanger, "Journal of Experimental Medicine," 1905, vii., 1906, 

 viii., and "American Journal of Physiology," 1906, xv. and xvi. 



