ACCELERANS IN THE FBOG. 67 1 



parts, after this operation, the heart- beats are still, increased in number, so that this increase 

 cannot be due to the increased blood-pressure. Indirectly it may be shown, by dividing or 

 extirpating all the nerves of the cardiac plexus, or at least all the nerves going to the heart, 

 that stimulation . of the medulla oblongata, or cervical part of the spinal cord, no longer 

 causes an increased frequency of the heart's action to the same extent as before division of 

 these nerves. The slightly increased frequency in this case is due to the increased blood- 

 pressure. 



The accelerating centre is certainly not continually in a state of tonic excitement, 

 as section of the aecelerans nerve does not cause slowing of the action of the heart; 

 the same is true of destruction of the medulla oblongata or of the cervical spinal 

 cord. In the latter case, the splanchnic nerves must be divided beforehand, to 

 avoid the slowing effect on the action of the heart produced by the great fall of the 

 blood-pressure consequent upon destruction of the cord, otherwise we might be apt 

 to ascribe the result to the action of the accelerating centre, when it is in reality 

 due to the diminished blood-pressure (C yon). 



According to the results of the older observers (v. Bezold and others), some 

 accelerating fibres run in the cervical sympathetic. A few fibres pass through the 

 vagus to reach the heart ( 352, 7), and when they are stimulated, either the heart- 

 beat is accelerated or the cardiac contractions strengthened {Heidenhain and. Lbwit), 

 or the latter alone occurs (Pawlow). The inhibitory fibres of the vagus lose their 

 excitability more readily than the accelerating fibres, but the vagus fibres are more 

 excitable than those of the aecelerans. 



Tarchanoff has described some very rare cases of individuals who, by a merely voluntary effort, 

 and while at rest, the respirations remaining unaffected, could nearly double the number of 

 their pulse-beats. 



Modifying Conditions. When the peripheral end of the nervus aecelerans is stimulated, a 

 considerable time elapses before the effect upon the frequency of the heart takes place, i.e., it 

 has a long latent period. Further, the acceleration thus produced disappears gradually. If 

 the vagus and aecelerans fibres be stimulated simultaneously, only the inhibitory action of the 

 vagus is manifested. If, while the aecelerans is being stimulated, the vagus be suddenly excited, 

 there is a prompt diminution in the number of the heart-beats ; and if the stimulation of the 

 vagus is stopped, the accelerating effect of the aecelerans is again rapidly manifested (C. Ludwig 

 with Schmiedebery , Bowditch, Baxt). According to the experiments of Strieker and Wagner 

 on dogs, with both vagi divided, a diminution of the number of the heart-beats occurred 

 when both accelerantes were divided. This would indicate a tonic innervation of the latter 

 nerves. 



[Aecelerans in the Frog. Gaskell showed that stimulation of the vagus 

 might produce two opposing effects ; the one of the nature of inhibition, the other 

 of augmentation. In the crocodile, the aecelerans fibres leave the sympathetic 

 chain at the large ganglion corresponding to the ganglion stellatum of the dog, and 

 run along the vertebral artery up to the superior vena cava, and, after anastomosing 

 with branches of the vagus, pass to the heart. " Stimulation of these fibres in- 

 creases the rate of the cardiac rhythm, and augments the force oi auricular con- 

 tractions; while stimulation of the vagus slows the rhythm, and diminishes the 

 strength of the auricular contractions." The strength of the ventricular contraction, 

 both in the tortoise and crocodile, does not seem to be influenced by stimulation of 

 the vagus, and probably also it is unaffected by the sympathetic. The so-called 

 vagus of the frog, in reality, consists of pure vagus fibres and sympathetic fibres, 

 and is in fact a vago-sympathetic. Gaskell finds that stimulation of the sympat/ietic, 

 before it joins the combined ganglion of the sympathetic and vagus, produces purely 

 augmentor or accelerating effects ; while stimulation of the vagus, before it enters 

 the ganglion, produces purely inhibitory effects. The two sets of fibres are quite 

 distinct, so that in the frog, the sympathetic is a purely augmentor (accelerator), 

 and the vagus a purely inhibitory nerve. Acceleration is merely one of the effects 

 produced by stimulation of these nerves ; hence, Gaskell suggests that they ought 

 to be called " augmentor," or simply cardiac sympathetic nerves.] 



[In his more recent researches Gaskell asserts that vagus stimulation produces first an inhibi- 



