ACTION OF THE HEART. 315 



ferior cervical and first dorsal ganglia of the sympathetic. Irritation of the 

 spinal cord itself, and of the medulla oblongata, causes increased frequency 

 of the pulse, though this has been shown by Ludwig and Thiry to be a com- 

 plicated phenomenon, and due in part to the effect of such irritation in 

 producing contraction of the smaller arteries. The accelerating fibres, 

 however, seemed from these observations to arise from centres in the me- 

 dulla oblongata and spinal cord, and emerging from the latter by the rami 

 commuuicautes to enter the sympathetic ganglia, and to proceed from 

 thence to the heart (see Fig. 126, right, side). This view is supported by 

 the experiments of v. Bezold and the brothers Cyon, 1 who have eliminated 

 the influence of vascular innervatiou by division of the spinal cord between 

 the first and second dorsal vertebra. The vessels are then permanently 

 paralyzed ; but irritation of the spinal cord in the cervical region will still 

 be found to produce considerable increase in the frequency of the pulse, 

 though the variations of blood-pressure are slight or nil. The course of the 

 accelerating fibres has been much elucidated by the recent careful dissections 

 of Schmiedeberg 2 made upon the dog. In this animal the vagus and 

 sympathetic run together as far as the inferior cervical ganglion. Here 

 they separate, and the vagus immediately gives off the recurrent laryugeal. 

 The last cervical and first dorsal ganglion of the sympathetics are con- 

 nected by two filaments, the upper one of which often joins the vagus. The 

 inferior cervical ganglion gives off the superior cardiac nerve, and some- 

 times the inferior cardiac, though both not unfrequeutly come off from the 

 vagus. One of them is sometimes absent, and both appear to act as accel- 

 erators (though they sometimes contain inhibitory fibres), and to reach the 

 sympathetic through the roots connecting the sympathetic with the cord. 

 In the rabbit, the fibres directly accelerating the action of the heart proceed 

 from the medulla oblongata, or possibly from the brain, and descending 

 through the cervical portion of the cord, emerge as in the dog, opposite the 

 inferior cervical and first dorsal ganglion of the sympathetic, which they 

 enter, and then proceed to the heart. In the Frog the vagus contains ac- 

 celerating as well as inhibitory fibres, for Wu'ndt 3 has shown that, at a 

 certain stage of poisoning with Woorara, irritation of the vagus no longer 

 caused slowing but quickening of the heart's action; and the same has been 

 noticed in the action of Atropin and Nicotin. On grounds similar to those 

 which have led to the admission of an intracardiac inhibitory centre, the 

 existence of an intracardiac accelerator centre, or series of centres, seems 

 probable. The accelerating fibres appear to be less easily excited and less 

 readily exhausted than the inhibitory fibres. 4 They render the contractions 

 of the heart more forcible as well as more frequent. 5 



246. During the last few years, the action of numerous poisons on the 

 heart has been made a subject of special investigation, but the results at 

 present obtained scarcely admit of being accurately classified. Some appear 

 to act as paralyzers, others as excitors of the motor and inhibitory nerves 

 respectively ; others, as the sulphocyanide of potassium, 6 act directly on the 



1 Arc-hiv f. Anat. and Physiol., 1867. 



2 Ludwig's Arbeiten. Bd. vi, 1871, p. 34. 



3 Yerhand des Naturhist. Med. Ver. zu Heidelberg, 1859. 



4 Schiff (Centralblatt, 1873, Nos. 1, 2, 3) denies the existence of accelerator fibre.?, 

 both in the sympathetic and the cervical portion of the spinal cord. He derives the 

 accelerator fibres from the spinal accessory nerve, and maintains that they run in the 

 vagus. 



5 Badoud, Verhancl. d. Phys. Med. Gesellsch. zu "Wiirzburg, N. F., Bd. viii, p. 12. 



6 C. Bernard, Lesons sur les Substances Toxiques, etc., 1857, p. 358; MM. Olli- 

 vier and Bergeron in Brown-Sequard's Journal de la Physiol., 1863, pp. 35 and 47, 

 and MM. Dubreuil and Legros, Comptes Eendus, 1867, p. 1256. 



