204 



THE CONTRACTION OF CARDIAC MUSCLE. 



Time in Seconds 



in 1869, Coats 1 pointed out that the contractions of the heart registered 

 by a mercurial manometer were markedly diminished in force upon stimu- 

 lation of the vagus nerve. These observations were followed by those of 

 Nuel, 2 who observed that the contractions of the auricle were diminished 

 to a greater extent than those of the ventricle, and were afterwards con- 

 firmed both by myself and Heidenhain in 1881 and 1882. This very 

 fact, that a diminution in strength of contraction as well as in rate, 

 taken in connection with the observed fact that the force of the cardiac 

 contraction does not vary with the strength of the stimulus, ought of itself 

 to have been sufficient to convince physiologists that the inhibitory nerve 

 acts on the muscle itself, and not by diminishing a stimulus from motor 

 ganglia. So strong, however, is the incubus of a dominant theory, 

 that even up to this day the action of the vagus nerve is spoken of as 

 diminishing impulses to the muscle rather than as affecting the muscle 

 itself. 



Quite early in the investigation of the action of the vagus nerve on 

 -, the heart, Schiff 3 



pointed out that the 

 muscular tissue, both 

 of auricle and ven- 

 tricle, in the frog, 

 responded less readily 

 to a stimulus during 

 standstill, or even 

 would not respond 

 at all, although the 

 stimulus was a strong- 

 one. This was con- 

 firmed by Eckhard, 4 

 and is now univer- 

 sally allowed, and is 

 evidence that the 

 vagus nerve di- 

 minishes the excita- 

 bility of the muscular 

 tissue. 



ISext came the 



work of myself and Heidenhain, which showed the necessity of 

 separating the inhibitory from the accelerator fibres in the frog's 

 vago-accelerator nerve, in order to obtain the pure effects of inhibitory 

 action. The contrast between the stimulation of the vagus in the frog 

 or toad, as ordinarily given, and that of its two components, the intra- 

 cranial vagus on the one hand and the sympathetic on the other, is given 

 in Figs. 108, 109, 110, 111, 112, 113; and in my paper in the Philo- 

 sophical Transactions, a number of tracings show how variable is the 

 extent of the inhibitory effect when the augmentor fibres are stimulated 

 simultaneously. In my experiments upon the effect of stimulation of 

 the intracranial vagus, I have been struck with three phenomena, 5 which 



1 Ber. d. k. Sachs. Gesellsch. d. Wissensch. , Leipzig, 1869, S. 360. 



2 Arch. f. d. ges. Physiol., Bonn, 1874, Bd. ix. S. 83. 



3 "Modus der Hcrzbewegnng," Arch./, physiol. Hcilk., Stuttgart, 1850. 



4 " Erregung des durch Vagusreizung zuni Stillstand gebrachten Herzen," Bcifr. ~. Anat. 

 u. Physiol. {Eckhard), Giessen, 1883, Bd. x. S. 23. 



5 Trans. Intcrnat. Med. Cong., Copenhagen, 1884, Section of Physiol., p. 29. 



IAA/WV 



Ventricle 



Fig. 108. — Heart of toad. Suspension method. Clamp in 

 auriculo- ventricular junction. Weak stimulation of the 

 intracranial roots of the vagus nerve. 



