2oo THE CONTRACTION OF CARDIAC MUSCLE. 



plexus, and that in this animal a regular annulus of Yieussens, strictly 

 corresponding to the arrangement in mammals, existed. I then care- 

 fully investigated the sympathetic system of the frog and toad, 1 feeling 

 sure that they could not prove an exception, and found that from the 

 ganglion on the third nerve, i.e. the first postbrachial nerve, an annulus 

 of Vieussens passed to the ganglion on the second nerve, i.e. the brachial 

 plexus, and from thence the sympathetic nerve passed to the vagus at 

 the region of the vagus ganglion, some of the fibres turning back with 

 the vagus to go to the heart, while others went on to the Gasserian 

 ganglion of the trigeminal. Here, then, was precisely the same arrange- 

 ment as in the mammal or tortoise, and the experiment showed that stimu- 

 lation of any part of the course of these fibres, between the anterior 

 roots of the third nerve and the vagus ganglion, gave pure augmentor 

 and accelerator effects ; while, on the other hand, stimulation of the roots 

 of the vagus within the cranium gave pure inhibitory effects. 



Thus the proof was obtained that the innervation of the heart is the 

 same both in cold-blooded and warm-blooded animals. In all cases the 

 inhibitory fibres leave the central nervous system in the roots of the 

 vagus, while the augmentor fibres leave in the roots of the nerves 

 immediately succeeding those which form the brachial plexus ; and the 

 reason was clearly seen why Weber and others following him were 

 unable to find the accelerators in the frog, for they expected them to leave 

 by the third or fourth ganglion and go direct to the aorta, and so to the 

 heart ; they were therefore stimulating the nerve in the wrong direction. 



In the course of these investigations I was struck with the histological 

 difference between the two sets of nerves on their way to the heart ; the 

 inhibitory nerves of the vagus being medullated, while those of the 

 accelerator were non-medullated. This led to the investigation of the 

 histological nature of the accelerator nerves in the whole of their course, 

 and to the conclusion that both inhibitory and accelerator nerves 

 belonged to the great system of efferent ganglionated nerves ; a system 

 characterised by the fineness of their fibres, which are always medullated 

 when they leave the central nervous system, by the presence on each 

 one of these fine medullated fibres, in some part or other of its course, of 

 a ganglion cell, from which fibres of the same physiological character 

 pass to the end-organ. This system includes, not only the cells of the 

 sympathetic system, but all vagrant motor cells, such as are found on the 

 course of the accessory part of the vagus in the ganglion trunci vagi, on the 

 course of the third nerve in the ciliary ganglion, etc. The fibres which 

 pass from these cells are, in the majority of cases, non-medullated. 2 

 Seeing, then, that the vagus fibres entered the heart as medullated fibres, 

 and that no medullated fibres are to be found in the ventricle proper or 

 auricles, but only non-medullated, it was immediately evident that the 

 ganglion cells in the heart had the same relation to the medullated 

 inhibitory fibres of the vagus, as the ganglion cells of the ganglion stella- 

 tum to the medullated accelerator fibres in the white rami communi- 

 cantes, from the second, third, and fourth thoracic nerves. In other 

 words, the intrinsic cardiac ganglion cells belong to the same system as 

 the extrinsic cardiac and vasomotor ganglion cells, and there is no 

 justification whatever for ascribing special central nervous system 



1 Gaskell and Gadow, Journ. Physiol., Cambridge and London, 1884, vol. v. p. 362. 



2 Gaskell, "On the Structure, Distribution, and Function of the Nerves which innervate 

 the Visceral and Vascular System," Journ. Physiol., Cambridge and London, 1885, vol. vii. 



