442 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



distinguishes the remainder of the heart. This view is further supported by 

 the observation that a slight stimulus applied to the base of a resting ventricle 

 will often provoke a series of contractions, while the same stimulus applied to 

 the apex will cause but a single contraction. 1 



The action of muscariu on the heart is often held to indicate the nervous 

 origin of the heart-beat. Muscarm arrests the heart of the frog and other 

 vertebrates, but has no similar action on any other muscle either striped or 

 smooth, nor does it arrest the heart of insects and mollusks. It follows that 

 muscarin does not cause arrest by acting directly upon the contractile material 

 of the heart. The contractile material being excluded, the assumption of a 

 nervous mechanism on the integrity of which the heart-beat depends seems 

 necessary to explain the effect of the poison. 2 



Further arguments are based on uncertain analogies between the heart and 

 other rhythmically contracting organs. 



Muscular Theory of Heart-beat. The evidence just stated cannot be re- 

 garded as proof of the nervous origin of the heart-beat. The most that can 

 be claimed is that it makes such a conception plausible. Even this claim has 

 been denied by not a few investigators who believe that the heart-beat is a 

 purely muscular phenomenon. Here again the properties of the apex are con- 

 sidered to be of the first importance. It has been shown that a strip of muscle 

 cut from the apex of the tortoise ventricle and suspended in a moist chamber 

 begins in a few hours to beat apparently of its own accord with a regular but 

 slow rhythm, which has been seen to continue as long as thirty hours. If the 

 strip is cut into pieces and placed on moistened glass slides each piece will con- 

 tract rhythmically. 3 Yet in the apex of the heart no nerve-cells have been found. 



The apex of the batrachian heart will beat rhythmically in response to a 

 constant stimulus. Thus if the apex is suspended in normal saline solution 

 and a constant electrical current kept passing through it, beats will appear 

 after a time, the frequency of pulsation increasing with the strength of the 

 current. 4 Very strong currents cause tonic contraction. An apex made inac- 

 tive by Bernstein's crushing can be made to beat again by clamping the aorta 

 and thus raising the endocardiac pressure. 5 Chemical stimulation is also effect- 

 ive. Delphiuin, 6 quinine, 7 muscarin with atropin, 8 atropin alone, 9 morphin 

 and various other alkaloids, dilute mineral acids, dilute alkalies, bile, sodium 

 chloride, alcohol, and other bodies, 10 when painted on the resting ventricle, call 

 forth a longer or shorter series of beats. Stimulation with induction shocks 

 gives a similar result. 11 



1 Scherhey, 1880, p. 260. 2 Cushny, 1893, p. 451. 3 Gaskell, 1883, p. 54. 



* Bernstein, 1871, p. 230 ; Foster and Dewsmith, 1876, p. 737 ; von Basch, 1879, p. 71 ; Scher- 

 hey, 1880, p. 259; Langendorff, 1895, p. 336; Kaiser, 1895, p. 464. 



5 Gaskell, 1880, p. 51 ; Aubert, 1881, p. 366; Ludwig and Luchsinger, 1881, p. 231 ; Dastre, 

 1882, p. 458 ; Biedermann, 1884, p. 24 ; Langendorff, 1884, p. 6. 



6 Bowditch, 1871, p. 169. 7 Schtschepotjew, 1879, p. 56. 8 v. Basch, 1879, p. 73. 

 9 Lowit, 1881, p. 447. 10 Langendorff, 1884, p. 21 ; 1895, p. 333; Kaiser, 1895, p. 6. 



11 Bowditch, 1871, p. 149 ; Kronecker, 1875, p. 178 ; 1879, p. 381 ; 1880, p. 285 ; v. Basch, 

 1879, p. 71 ; Eanvier, 1880, p. 46; Dastre, 1882, p. 433; Gaskell, 1883, p. 52. 



