1884.] Reflex Action of the Cardiac Nerves in Fishes. 41 



mechanical or electrical stimulation of the skin of the head, or by 

 very slight stimulation of the gill apertures or of the mucous mem- 

 brane of the mouth. Weak irritation, which formerly produced 

 striking results, now seems to have no effect on these parts. Cardiac 

 inhibition and reflex contractions of the skeletal muscles may still be 

 excited by severe injury of the parts mentioned, or by ordinary 

 stimulation of the gills, tail, parietal peritoneum, first spinal nerve, or 

 trunk of the vagus nerve where it lies on the gullet. 



When the heart has been acting very slowly (in consequence of the 

 controlling influence of the central nervous system) prior to the admin- 

 istration of ether, the rate of action usually increases to a very 

 marked extent even when the amount of ether used has not yet been 

 enough to paralyse the reflex activity of the medulla, but when it has 

 induced a condition similar to that seen on removal of the optic lobes. 



It will be seen from the experiments described, that reflex inhibition 

 of the eel's heart is often excited by peripheral stimulation which 

 leads at the same time to reflex action of the skeletal muscles. The 

 vagus medullary centre is often thrown into a state of activity by 

 impulses which at the same time set into activity the motor centres of 

 the medulla and cord generally. Such results may be brought about 

 by stimulation of the skin of the head or tail, by stimulation of the 

 gill apertures, or of the mucous membrane of the mouth, and by 

 severe injury of any part of the body excepting the abdominal 

 organs. 



On the other hand, stimulation of certain parts can lead to cardiac 

 inhibition without any other indications of reflex action. The 

 medullary vagus centre may as a result of peripheral stimulation be 

 thrown into a state of excitement without the participation of any of 

 the motor centres of the medulla or cord ; sometimes with the 

 participation of one or more of the neighbouring medullary centres 

 {e.g., the respiratory). Such results are commonly obtained by 

 stimulation of the gills, of the fifth bronchial arch, of the first spinal 

 nerve, or of the vagus nerve as it passes along the oesophagus below 

 the heart. Stimulation of these parts frequently leads to prolonged 

 inhibition of the heart without the occurrence of any other indication 

 of reflex action. 



(In the case of all the animals experimented on, the brain was 

 destroyed or ansesthetics were administered before any operative 

 proceedings were resorted to.) 



