THE CAKDIAC CYCLE (rEVOLUTIO CORDIS) 275 



thorough emptying of the different chambers of the heart. But, as it 

 has been shown that single narrow segments of cardiac muscle give 

 typical twitch-Uke contractions, it must be concluded that the tetanic 

 character of the systoUc movement of the entire organ can only be 

 due to the fact that its different segments contract successively in 

 the direction from base to apex.^ 



The Speed of the Contraction Wave. — The progressive character 

 of the contraction of the heart may be studied best in the lower forms 

 in which the systole of the sinus antecedes that of the auricle, and the 

 systole of the latter that of the ventricle. In a similar way it may be 

 observed in the mammaUan heart that the auricular contraction is 

 separated from the ventricular by a definite interval which becomes 

 especially noticeable in an organ shortly before it ceases to beat. 

 A graphic record of the contraction wave may be made by placing 

 long writing levers upon the basal and apical portions of an exposed 

 heart. If these levers are permitted to write in the same vertical line 

 and in relation with a chronograph registering the time in seconds, it 

 is a simple matter to compute its speed, because the distance between 

 the levers can be measured directly with a ruler. In this way, it has 

 been found by Reid and Waller^ that the velocity of this wave is 10 cm. 

 in a second in the heart of the frog and 80 cm. per second in that of the 

 sheep. Bayhss and StarUng^ give the value of 300 cm. in a second for 

 the dog's heart. In accordance with these figures, it must be con- 

 cluded that the wave consumes at least 0.05 sec. in its passage across 

 the human heart. In fact, upon the basis of electrical measurements 

 made by Kraus and Nicolai,^ an even longer time seems to be required, 

 namely about 0.2 sec, before the distalmost segments of the ventricles 

 beconie involved. 



The Path of the Contraction Wave. — In the mammalian heart, the 

 musculature of the ventricles is completely separated from that of the 

 auricles by a zone of fibrous tissue.^ At one point, however, the two 

 masses are connected by a strand of modified muscle tissue which is 

 known as the bundle of His® or the auriculoventricular bundle. This 

 bridge begins in the basal portion of the interauricular septum, di- 

 rectly above the septum fibrosum atrioventriculare. It arises in a 

 complex nodular accumulation of cells and fibers which is usually re- 



1 Walther, Pfliiger's Archiv, Ixxviii, 1900, 597. 



2Phila. transactions, 198, 1888, 230. 



3 Proc. Royal Soc, 1892, 211. 



^ Berliner Klin. Wochenschr., 1907, Nr. 25 and 27. 



^ It has been known for some time that muscular connections between the 

 auricles and ventricles are present in the fish, reptiles and amphibians. The 

 existence of similar connections in mammals has been denied until 1893, when 

 G. Paladino and Stanley Kent put forth the claim that a path of this kind exists. 

 Their observations, however, cannot be regarded as valid, because their descriptions 

 are very indefinite, while the illustrations, showing certain connections between the 

 left auricle and ventricle, apparently do not picture the conditions as they actually 

 are. 



« Named after W. His, Jr. (1893), Professor of Anatomy at Leipzig (1863). 



