142 Canadian Record of Science. 



Influences Affecting the Natural Rythm of the Heart. Among 

 these, in addition to mechanical excitation inducing a re- 

 versed rythm already referred to, must be especially men- 

 tioned the condition of the blood supplying the heart as to 

 degree of oxidation. Blood, poor in oxygen, with greater 

 readiness than in other cold-blooded animals, causes irregu- 

 larity or arrest of the heart in a fish. 



Faradisation of the heart in the fish leads to results very 

 closely allied to those obtained in the Chelonians. 



Reflex Cardiac Inhibition. The ease with which the heart 

 of a fish can be reflexly inhibited by the stimulation of 

 various parts of its body, is one of the most remarkable 

 facts brought out by investigation on the heart physiology 

 of the animal. 



The results are much the same whether mechanical or 

 electrical stimuJation with the rapidly interrupted current 

 be employed. The parts that have been found most effective 

 in Batrachus are the gills, the air bladder, the abdominal 

 viscera, the mucus lining of the mouth, the tentacular appen- 

 dages of the mouth, the pectoral fins, the anus and the tail. 



The results may be either (1) decided arrest of the heart 

 for several seconds, followed by a slowed rythm, or (2) brief 

 arrest of the slowed and irregular rhythm or (3) the latter 

 lasting from one to two minutes or longer without any actual 

 stop of the heart. In some cases the operative procedure 

 necessary to expose the heart is sufficient stimulus to keep 

 the heart long inhibited. , The results of inhibition are not 

 uniform. In some cases no acceleration seems to follow, but 

 in others and the majority, there is decided acceleration of 

 the rythm. 



Peculiar Results associated ivith Reflex Cardiac Inhibition. 

 Stimulation of several of the parts mentioned above, and 

 especially of the anus and tail, have given the following 

 results : 



(1.) At first an accelerated rhythm followed by a slowed 

 rhythm, or 



(2.) An accelerated rhythm followed by a slowed rhythm 

 on increasing the' current, or 



(3.) Only an accelerated rhythm. 



