UPON THE VASCULAR SYSTEM. 117 



degree of sensibility varies in different animals ; M, The preparation of the 

 nerve cannot, of course, be conducted so that precisely the same amount of 

 injury is inflicted upon it in different cases. When I first elicited the difference 

 between the results given in column A. and those in column B., it occurred to 

 me that possibly the inferior laryngeal nerve fibres are more excitable than 

 those of other motor nerves. But a few experiments on rabbits and frogs satis- 

 fied me that such is not the case. It is to the last degree unlikely that the 

 inferior laryngeal nerve is more excitable than the inferior cardiac nerve, and, 

 therefore, I think, we must look to the peripheral terminations of the two 

 nerves for the explanation of the facts above given. An ordinary motor nerve 

 may be supposed to encounter little — if any — opposition when it acts upon the 

 muscular plasm, but the inhibitory nerve has to act on a nervous apparatus 

 in which there are counter-influences constantly at work. Only a powerful inhi- 

 bitory influence can hold these in check, and indeed so powerful are these 

 promptings to motion within the heart, that stimulation, however strong, of the 

 inhibitory nerve, cannot keep the heart quite still for more than a few seconds. 



Having, in the above manner,"" entirely failed to find any acceleration of the 

 heart follow stimulation of the vagus, another method of experimentation 

 suggested itself to my mind. It has been shown by Botkin that atropia 

 paralyses the cardio-inhibitory fibres of the vagus, that is to say, it so affects 

 them or their terminations in the heart, that when they are stimulated the 

 frequency of the pulse is no longer diminished.t I determined to produce this 

 paralysis, and then see whether or not acceleration of the heart's action followed 

 irritation of the lower end of the vagus. 



Experiment XVII. — In a rabbit I divided both vagi in the neck, and stimu- 

 lated the lower end of the right vagus by a powerful current (Secondary 40 mm. 

 distant from primary coil of induction machine. One Daniell). The heart's 

 action was arrested. I then injected ten milligrammes of atropia sulphate into 

 the jugular vein. When two minutes had elapsed, I stimulated the same nerve 

 with a current of the same strength. The heart's action, instead of being 

 arrested as before, was slightly accelerated. Before stimulation of the nerve, 

 the pulse in 20" numbered 90 — during stimulation it numbered 96. After an 

 interval of four minutes, I stimulated the nerve again with the same current. 

 Before stimulation the pulse was 104 in 20" — during stimulation it rose to 

 112. After a further lapse of time, I excited the lower end of the left vagus in 

 the same manner, but no acceleration of the pulse ensued. The acceleration of 



* Should the reader at any time have occasion to repeat the above experiments, he will require to 

 observe the arytenoid cartilages very narrowly, in order to detect the finest movements which may re- 

 sult from irritation of the vagus. The animal should be arranged so that the light may be reflected 

 from the inner surface of the arytenoid cartdage. The slightest movement of the glittering mucous 

 surface can then be readily detected. 



t Vihchow's Archivs, Band xxiv., 1862, p. 89. 



