PROPERTIES OF THE HEART MUSCLE. 581 



frog's heart, in which the contraction begins in the sinus venosus, 

 spreads to the auricles, thence to the ventricle, and finally 

 to the bulbus arteriosus. Under normal conditions this sequence 

 is never reversed, and an explanation of the natural order 

 forms obviously an important part of any complete theory 

 of the heart beat. Those who hold to the neurogenic theory 

 naturally explain the sequence of the beat by reference to the 

 intrinsic nervous apparatus. If the motor ganglia lie toward the 

 venous end of the heart one can imagine that their discharges may 

 affect the different chambers., in sequence, the pause between 

 auricular and ventricular contraction being due, let us say, to the 

 fact that the motor impulses to the' ventricle have to act through 

 subordinate nerve cells in the auriculo-ventricular region, and the 

 time necessary for this action brings the ventricular contraction 

 a certain interval later than that of the auricle. There is no 

 immediate proof or disproof of such a view. The numerous exper- 

 iments made upon the rapidity of conduction of the wave of 

 contraction over the heart are not conclusive either for or against 

 the view. The fact, however, that in the quiescent but still irritable 

 heart the rhythm may be reversed by artificially stimulating the 

 ventricle first seems to the author to speak strongly against the 

 dependence of the sequence upon any definite arrangement of 

 neuron complexes. On the myogenic theory the sequence of the 

 heart beat is accounted for readily by relatively simple assumptions. 

 Gaskell and Engelmann have each laid emphasis upon the facts in 

 this connection, and the application of the myogenic theory to the 

 explanation of the normal sequence of contractions forms one of its 

 most attractive features. Gaskell assumes* that the rhythmical 

 power of the muscle at the venous end is greater than that at the 

 ventricular end, that is, if pieces from the two ends are examined 

 separately it will be found that the spontaneous rhythm of the 

 tissue from the venous end is more rapid. This portion of the 

 heart, therefore, beating more rapidly, sets the rhythm for the 

 whole organ, since a contraction started at the venous end will 

 propagate itself from chamber to chamber. That each chamber of 

 the heart has a rhythm of its own and that the rhythm of the ven- 

 ous end is the more rapid and constitutes the rhythm of the intact 

 heart has been shown in various ways upon the hearts of different 

 animals. Thus, Tigerstedt has devised an instrument, the atrio- 

 tome,t by means of which the connections between auricle and 

 ventricle may be crushed without hemorrhage. Under such condi- 

 tions the ventricle continues to beat, but with a much slower rhythm 

 and with a rhythm entirely independent of that of the auricles. 



* Gaskell, "Journal of Physiology," 4, 61, 1883; also vol. ii, p. 180, of 

 Sehafer's "Text-book of Physiology," 1900. 



t See "Lehrbuch der Physiologic des Kreislaufes," 1893. 



