38 



Dr. J. A. McWilliam. On the 



[Dec. 18, 



originates from the bunch of nerves which make up the vagus. It 

 separates from the other portions of the vagus near the skull ; it then 

 passes along the lateral surface of the animal, pursuing the same 

 general course as the lateral line, though for the greater part of its 

 course at a considerable depth from the surface, embedded among the 

 muscles. In the eel it does not extend to the tail, as it does in some 

 fishes (e.g., carp) ; it terminates at a variable point, sometimes about 

 the junction of the caudal third with the rest of the body, sometimes 

 in the middle third of the animal's length. 



Section of this nerve is followed by no visible effect. And stimula- 

 tion of its central end seems to exert no marked influence on the 

 cardiac action. 



The sudden placing of an eel in the vertical position with the head 

 downwards, sometimes leads to a temporary cardiac arrest, provided 

 the circulation be intact. Movements of the animal occur at the same 

 time as the inhibition of the heart, and when no such movements 

 result from the placing of the animal in the position referred to, the 

 cardiac inhibition also fails to occur. And even in the cases where 

 cardiac inhibition (accompanied by movements of the animal) does 

 occur, the inhibition is usually a very temporary one. The heart is 

 not kept at a slow rate during the whole time that the vertical 

 position is maintained ; in fact, there is generally, after a little time, 

 a slight acceleration of the heart's rhythm beyond what was seen when 

 the animal was in the horizontal position. In the vertical position 

 (with the head downwards) the heart is much distended with blood, 

 and fails to empty itself at each beat. And section of both vagi does 

 not seem to have any effect upon the gorged condition or slightly 

 accelerated rate which the heart exhibits while the above-mentioned 

 position of the animal is maintained. 



When the eel is held in a vertical position with the head upwards, 

 the heart becomes small, pale, and empty, or almost empty. Its rate 

 of action remains unchanged, or after a little time becomes somewhat 

 slower than in the horizontal position ; the latter result (a somewhat 

 slowed rate) seems to be the one that more commonly occurs. 



Reflex arrest of the heart — brought about in any of the ways 

 mentioned — does not depend upon alterations in blood-pressure. It 

 occurs after section of all the large blood-vessels. 



The eel's brain can be readily exposed by removing the cranial roof 

 by means of a pair of strong scissors or a bone forceps. The effects 

 of stimulation and removal of the various parts can then be tested. 



Stimulation of the cerebral hemispheres has no apparent effect 

 either with regard to the condition of the heart or of the skeletal 

 muscles. And removal of these parts seems to have no marked 

 effect. 



Stimulation of the optic lobes leads to very striking results ; the 



