1884.] Reflex Action of the Cardiac Nerves in Fishes. 37 



probably caused by Marshall Hall's blow upon the stomach, and to 

 such jarring may, it seems to me, with most probability, be attributed 

 the cardio-inhibitory phenomenon which he describes. 



Stimulation of the air-bladder and the other abdominal organs 

 appears to be without effect on the heart's action. The abdominal 

 organs seem, in fact, to be the only parts of the animal from which 

 cardiac inhibition cannot by powerful stimulation be excited. And 

 similarly with regard to reflex movements, little or no effect is mani- 

 fested in response to the most powerful stimulation of the abdominal 

 organs. 



Stimulation of the abdominal sympathetic nerves seems to have no 

 influence on the cardiac action. 



Stimulation of the central end of the right or left vagus nerve below 

 the origin of the cardiac branch causes well-marked reflex inhibition, 

 provided the nerve be stimulated in that part of its course where it 

 lies along the gullet. Stimulation of either vagus nerve below the 

 gullet, i.e., after the nerve has passed from the gullet on to the 

 stomach, seems to have no cardio-inhibitory effect. Stimulation of 

 the inner and outer surfaces of the gullet itself appears to be without 

 effect on the heart ; whilst the application of a very weak current to 

 the vagus nerve lying along its outer surface, most readily brings 

 about a prolonged arrest of the cardiac action. 



Stimulation of the first spinal nerve, or any of its branches, gives 

 rise to marked inhibition of the heart. Many of the branches of this 

 nerve can be very easily isolated, as they pass to the muscles on the 

 ventral aspect of the body anterior to the pectoral fins. Stimulation 

 of the central end of any of the spinal nerves is often followed by 

 cardiac arrest. 



Irritation of the mucous membrane of the mouth seems in most 

 instances to lead to cardiac arrest. This can easily be shown by intro- 

 ducing any pointed instrument into the mouth and scratching the 

 mucous membrane. General muscular movements are usually induced 

 at the same time as the cardiac inhibition. 



Irritation of the pharynx seems to be still more effective as regards 

 its influence in suspending the cardiac action. 



Severe injury of almost any part of the animal — with the exception 

 of the abdominal organs — is usually followed by a more or less pro- 

 longed standstill of the heart. This result is generally accompanied 

 by more or less extensive and continued movements of the skeletal 

 muscles. Injury of the pectoral fins seems in many instances to be 

 more effective in causing reflex inhibition than does injury of the body 

 generally, excepting of course the specially effective parts {i.e., head, 

 tail, parietal peritoneum, and gills) already mentioned. 



I have on many occasions investigated the effect of stimulation of 

 the great lateral nerve upon the cardiac movements. This nerve 



