1884.] Reflex Action of the Cardiac Nerves in Fishes. 39 



heart stands still, while strong contraction of the skeletal muscles 

 occurs. These results are got by the application of very weak 

 interrupted currents ; and also by mechanical stimulation. The 

 effects produced do not seem to be due to a spreading of the 

 stimulating current to the medulla ; the currents used are extremely 

 weak, and, moreover, stimulation of the cerebellum (which lies much 

 nearer the medulla than do the optic lobes) gives no effect at all or 

 only a very trivial effect compared to that obtained from the optic 

 lobes. If the interrupted current applied to the optic lobes spread to 

 the medulla, it ought surely to spread as readily or indeed much 

 more readily to the medulla when applied to the cerebellum. 



Removal of the optic lobes seems to lead to a change in the 

 readiness with which stimulation of certain parts leads to reflex 

 cardiac inhibition. The application of slight friction or weak 

 electrical currents to the skin of the head seems (after removal of the 

 optic lobes) to have no effect on the heart's action; neither does 

 slight irritation of the mucous membrane of the mouth, nor irritation 

 of the gill apertures. Very severe injury of any of these parts may 

 still, however, lead to cardiac inhibition. 



Removal of the optic lobes also seems in many instances to lead to 

 an acceleration of the rate of the heart's action. 



Stimulation of the medulla is highly effective in causing prolonged 

 suspension of the cardiac action. A rapidly interrupted current is not 

 essential ; a current witb interruptions at the rate of two or three per 

 second is effective. Removal of the medulla abolishes all the pheno- 

 mera of reflex cardiac inhibition. 



After removal or destruction of the medulla, the heart rhythm is 

 generally accelerated to a considerable extent. A similar change in 

 the rate of cardiac action can usually be observed as a consequence of 

 section of the vagi. It would seem then that during the time the 

 animal is experimented on with intact medulla and vagi, the heart's 

 action is under a continued controlling influence which renders its 

 rhythm slower than it would be were it not for this controlling 

 influence exerted by the medulla upon the heart through the medium 

 of the vagi nerves. And this controlling influence is manifested when 

 the eel is left uninterfered with for a considerable time, and when 

 the animal appears to be in a perfectly quiescent state. However, the 

 means which are employed to fix the animal, and the incisions which 

 have been made to expose the heart and brain, may be sources of 

 irritation which by sending afferent impulses to the medulla, keep the 

 vagus centre in a state of slight but continued activity. And if 

 extensive injuries have been inflicted, e.g., if the animal is cut across 

 at the middle of its length, the continued controlling influence 

 exerted by the central nervous organs on the heart is, as a rule, 

 decidedly more marked. This controlling influence is much more 



