578 CIRCULATION OF BLOOD AND LYMPH. 



of that of the auricles. When the compression is removed the ven- 

 tricle falls in again with auricular rhythm. By variations in the 

 pressure upon the bundle intermediate conditions may be obtained 

 in which the "block" between auricle and ventricle is only partial, 

 and in which, therefore, the ventricular systole follows regularly 

 every second or third auricular contraction. When the "block" is 

 complete the ventricular rhythm ceases to have any definite rela- 

 tionship to that of the auricle, it beats entirely independently and 

 its rate is slower than that of the auricle. It is interesting to re- 

 member that cases of complete or partial heart block occur in man. 

 In the condition known as the Stokes- Adams syndrome the striking 

 feature in addition to attacks of syncope is a permanently slowed 

 pulse, the heart bea c falling to 30 or 20 beats per minute or lower. 

 Erlanger has shown that in such cases there may be complete or 

 partial heart block. In the former condition the rhythm of the 

 ventricle is entirely independent of that of the auricle and of course 

 much slower. The ventricles may be beating at 27 per minute and 

 the auricles at 90. In partial block the ratio between the ventric- 

 ular and auricular rate is definite, every second or third auricular 

 beat being followed by a ventricular systole (see Fig. 237). In a 

 number of these cases it has been shown at autopsy that there was 

 a distinct lesion involving the auriculoventricular bundle, but in 

 other cases lesions of this kind have not been discoverable.* 



Fig. 237. 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. 



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 



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

 viii., and "American Journal of Physiology," 1906, xv. and xvi. For the litera- 

 ture upon autopsies in cases of Stokes-Adams' disease consult Krumbhaar, 

 "Bulletin of the Ayer Clinical Laboratory," Philadelphia, No. 6, 1910, and 

 Bachmann, "Journal of Exp. Medicine," 16, 41, 1912. 



