THE HEART 139 



regularly must always be as long as twice the ordinary 

 pulse interval (Fig. 5). Those of auricular origin 

 may be of this length, but are not usually so ; for the 

 irritability of the auricle increases so fast during quies- 

 cence that it is not likely to wait so long before passing 

 again into contraction (Fig. 6). On the other hand, 

 all intermissions less than two beats in duration are not 

 necessarily due to disease in the auricular fibres, for 

 some of them may be brought about by excessive vagus 

 control, which actually stops the heart for a moment. 

 This form of intermission, however, is abolished by 

 atropine, and can be recognized by that peculiarity.* 



' 84- ' 98 I 158 38 94 95 94- 97 



FIG, 6, PULSE TRACING, SHOWING AURICULAR INTERMISSION. 

 (AFTER CUSHNY.) 



The intermission, 158, is much less than twice the length of the 

 preceding pulse. 



As a matter of clinical experience, irregularity of the 

 heart seems specially prone to occur when the auricle is 

 diseased.! Such irregularity proceeding from the auto- 

 matic contractile fibres is of more serious import than 

 that due to alterations in conductivity or lowered ven- 



* Cushny, ' On the Interpretation of Pulse Tracings,' Journ. of 

 Exper. Med., 1899, vol. iv., p. 327, and Brit. Med. Journ., 

 1900, ii. 892. 



t Eadasewsky, Zeit. f. Klin. Med., 1895, xxvii. 381. 



