202 



THE CONTRACTION OF CARDIAC MUSCLE. 



we may formulate our present knowledge of the meaning of the ganglion 

 cells in the heart as follows : 



Efferent fibres of opposite function leave the central nervous system 

 to supply the viscera ; they pass out of the central nervous system as 

 the fine medullated processes of nerve cells in the central nervous system. 

 These nerve fibres, the pre-ganglionic fibres, do not pass directly into the 

 tissue of the peripheral organ, but each one terminates in connection 

 with an efferent nerve cell, from which a number of fibres, the post- 

 ganglionic fibres of the same physiological value, pass to the tissue. 

 The efferent nerve cells of the augmentor system are situated in the 

 ganglia of the so-called sympathetic system ; the corresponding efferent 

 nerve cells of the inhibitory system are situated in the heart itself. 



This simple explanation of the meaning of the cardiac ganglion cells, 

 combined with Langley's discovery that nicotine acts upon the junction 

 between the nerve fibre and its efferent cell, like curari upon the termina- 

 tion of the motor nerve in striated muscle, while it does not affect the 

 termination of the post-ganglionic nerve fibre in the end tissue, 

 immediately gives (as pointed out by Langley and Dickinson 1 ) a 

 straightforward explanation of Schelske's and Schmiedeberg's experi- 

 ment with respect to the action of the vagus nerve in the frog, after 

 curari and nicotine respectively ; for it is clear that in stimulating the 

 so-called vagus in this case, they were really stimulating the post- 

 ganglionic fibres of the augmentor system and the pre-ganglionic fibres 

 of the inhibitory system. The former fibres, therefore, were unaffected 

 by the poison, while the junction between the latter and their efferent 

 ganglion cells was interrupted, consequently acceleration and augmenta- 

 tion alone took place, although direct stimulation of the venous sinus 

 still caused standstill, because, with the electrodes in that position, 

 the post-ganglionic fibres from Eemak's ganglia were stimulated. 

 Atropine, on the other hand, prevented the inhibition upon direct stimula- 

 tion, because, as will be shown later, it paralyses the action of the 

 post-ganglionic fibres upon the muscular tissue. 



Again, the evidence that these intrinsic ganglion cells belong to the same 

 system as the extrinsic efferent ganglia, is borne out by the results of embryo- 

 logical investigation, which may be shortly summed up by saying that the 

 observations of Balfour 2 and Oiiodi 3 have led to the conclusion that the 

 sympathetic chain of ganglia is formed as offshoots from the spinal ganglia ; 

 and the recent observations of His, 4 and of His and Romberg, 5 have shown that 

 the same method of origin applies also to the cells in the heart itself. They 

 are found in connection with the vagus nerves as offshoots from the vagus 

 ganglia, at first outside the forming heart, and afterwards become included 

 within the heart itself. These workers further confirm previous observations, 

 to the effect that the heart has already begun to beat before the ganglion cells 

 have become included in its tissues. Although in most animals the intra- 

 cardiac ganglion cells belong to the vagus nerve, yet in some, especially in man, 

 according to His, they are chiefly derived from the sympathetic ganglia. If 

 such a difference really exists, then it is possible that in all animals a varying 

 number of fibres belonging to the augmentor nerves may not reach their 

 ganglion cell until they enter the heart itself. 



1 Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 277. 



2 "Comparative Embryology," vol. ii. p. 384. 



3 Arch. f. Anat. u. Entwcklngsyesch., Leipzig. 1884, S. 145. 



4 His, jun., Abhandl. d. k. Sachs. Gesellsch. d. Wissenxch., Xo. 1, Bd. xviii. 



5 Verhandl. d. ix. Cong.f. inncrc Med., Wiesbaden, 1890. 



