CAUSATION OF HEART-BEAT. 



187 



wave, just as in the hearts of the frog, tortoise, 1 eel, 2 etc. Further, 

 MacWilliam 3 has shown that in the mammalian, just as in the cold- 

 blooded heart, a reversal of the sequence takes place when the ventricle 

 is made to beat at a quicker rate than the great veins and auricles ; so 

 also does a block take place at the auriculo- ventricular junction, of 

 precisely the same character as in the cold-blooded, so that the ventricle 

 responds to every second contraction of the auricle, etc. Another 

 difference of a fundamental character was said to exist by Waller 

 and Eeid, 4 who concluded, from the measurement of the time relations 

 of the electrical variation at two points on the ventricle, that the apex 

 of the ventricle in the beat of the warm-blooded heart contracts before 

 the base, while in the beat of the cold-blooded the base contracts before 

 the apex. Bayliss and Starling, 5 however, have shown that this conclu- 

 sion is erroneous, and that the contraction travels over the mammalian 

 ventricle from base to apex, just as in the hearts of the frog and other 

 cold-blooded animals. 



With respect to the rhythmical power of the different parts of 

 the heart, we find the same results as in the cold-blooded, the main 

 difference being that the mammalian ventricle, when isolated, appears to 

 possess greater rhythmical power than that of cold-blooded animals. 

 Thus the observations of Wooldridge, 6 of Tigerstedt, 7 by means 

 of the atriotome, and of MacWilliam, 8 all show that the ventricle 

 when separated from the auricles beats immediately with its own 

 rhythm, without any marked preliminary standstill. The mammalian 

 heart, therefore, is said not to correspond to that of the cold-blooded 

 in this important respect, that the Stannius standstill does not exist. In 

 these experiments, it is important to remember one thing, namely, that 

 the circulation of blood in the ventricle is retained, in Wooldridge's 

 experiment, by the removal of the e*craseur; in Tigerstedt's, by the 

 application of the atriotome, while in the experiments upon cold-blooded 

 hearts, the ligature or section between sinus and ventricles removes 

 all blood supply from the ventricle. In the case of the tortoise, I have 

 to all intents and purposes seen the same result as described for the 

 mammalian heart, by means of the simple expedient of supplying 

 the ventricle with blood through its coronary system (as already 

 mentioned). Then, just as in the mammalian heart, the Stannius stand- 

 still is either cut short, or does not occur, and the ventricle commences 

 immediately upon isolation to beat with its own rhythm. In this 

 respect, then, the mammalian ventricle does not fundamentally differ 

 from that of the cold-blooded animal. 



Quite recently, still further proofs that the same explanation of the 

 cause of the heart-beat applies to the heart of the warm-blooded as to 

 that of the cold-blooded animal, has been given by Porter, 9 for he has 

 shown, in the first place, that the isolated strip from the ventricle of the 

 mammalian heart resembles that from the heart of the tortoise in its 



1 Gaskell, Journ. PhysioL, Cambridge and London, 1883, vol. iv. p. 70. 



2 MacWilliam, ibid., 1885, vol. vi. p. 195. 



3 Ibid., 1888, vol. ix. p. 185. 



4 Phil. Trans., London, 1887, p. 215. 



5 Proc. Roy. Soc. London, 1891. vol. iv. p. 211 ; and Intcrnat. Monatschr. J. Anat. u. 

 PhysioL, Leipzig, 1892, Bd. ix. 



>G Arch. f. PhysioL, Leipzig, 1883. 7 Ibid., 1884. 



s -0p. cit., p. 177. 



9 "On the Cause of the Heart-beat," Journ. Exp&r. Med., New York, 1897, vol. 11. p. 391. 



