THE CARDIAC CYCLE (rEVOLUTIO CORDIS) 279 



lished. Eventually, however, the ventricle develops a rhythm of its 

 own which is made possible by its inherent power of contraction. 

 This condition constitutes total heart-block. It must be remembered, 

 however, that there are also certain intermediate stages of this affec- 

 tion which arise whenever the obstruction is not complete. This en- 

 ables the wave of excitation to break through at intervals. Thus, it 

 may come to pass that only every second, or every third or fourth 

 auricular systole is able to elicit a regular ventricular contraction, 

 thus establishing a2:l, 3:1, or4:l rhythm. In other words, while 

 one single wave may not be sufficiently powerful to overcome the re- 

 sistance placed in the path of conduction, the sum total of two or three 

 or more may suffice to break through this obstruction. And naturally, 

 whenever the ventricle is thus made to respond to an auricular beat, 

 the resulting systole must exhibit the characteristics of a normal 

 contraction, because under ordinary conditions, the activity of cardiac 

 muscle does not vary with the strength of the stimulus, but remains 

 constant. 



It has been stated by Kent^ that these observations, although origi- 

 nally made upon the heart of the frog, may be duplicated in mammals, 

 but the evidence submitted in support of this statement cannot be re- 

 garded as at all convincing. In conformity with the work of Wool- 

 dridge and Tigerstedt,^ it has been found by His that the auricles and 

 ventricles may be functionally dissociated not only by destroying the 

 inter auricular septum, but also by causing a local injury to the auric- 

 uloventricular bundle. These results have been confirmed and much 

 extended by Erlanger.^ In man, heart-block commonly arises in con- 

 sequence of endocardial lesions or tumors involving the origin and main 

 strand in the bundle of His. It may also be caused by a general 

 diminution in the irritability of the ventricular musculature, a con- 

 dition which may result in the course of syphilis and septic infections 

 and intoxications. 



Fibrillation of the Cardiac Muscle (Delirium Cordis). — When 

 in fibrillation, the musculature does not respond with strong and 

 unified contractions, but with a continuous wavy and oscillatory 

 motion. This condition may be more or less localized or may affect 

 the organ as a whole. When restricted to the auricles, as it frequently 

 is, it is designated as auricular fibrillation, and when involving the 

 ventricles, as ventricular fibrillation. It follows strong electrical, 

 thermal, or mechanical stimulation of the cardiac muscle as well as 

 obstructions to the coronary circulation. It is scarcely possible to 

 relieve this condition after it has been firmly established. In this 

 regard, it differs from the so-called flutter which signifies an extreme 

 increase in frequency, sometimes to 300 or 400 in a minute without 

 marked alteration in the character of the individual beats. 



1 Jour, of Physiol., xiv, 1893, 233. 



2 Archiv fur Physiol., 1883 and 1884. 



. 3 Am. Jour, of Physiol., xvi, 1906, 160; and xxx, 1912, 395. 



