Physiology of the Heart. 143 



This subject is further treated iu the account of the turtle 

 and aliigator above. 



It should be noted that in the skate, stimulation along 

 certain lines on the ventral surface of the fish, apparently 

 the course of mucous glands and likely associated with 

 special sensitive structures, has produced remarkably good 

 cardiac inhibition, and the results have been constant. The 

 mucous membrane of the mouth, is also in the skate, a part 

 giving decided results. 



Independent Rhythm of Various Parts of the Heart. A 

 large number of experiments On both the isolated heart 

 and the heart in situ have brought out the following facts : 



(1.) There is very great variety in the hearts of different 

 fishes as to capacity for independent rhythm ; between such 

 fishes as the skate, the shark and the toadfish (Batrachus) 

 this difference is enormous. 



(2.) In Batrachus every part of the heart is capable of 

 good, independent rhythm ; even the apex of the heart when 

 isolated has shown such. 



(3.) The order of the parts of the heart with greatest 

 independent rhythmic power is — sinus, sinus extension, 

 auricle, ventricle. 



[4.] The independent rhythm of the ventricle begins soon 

 after its separation from the rest of the heart (by ligature), 

 speedily reaches a maximum and gradually declines. 



The Action of Certain Drugs and Poisons on the Heart. Ex 

 periments have been made on the heart in situ and the results 

 confirmed on the isolated heart. The agent was in each case 

 applied in solution directly to the heart itself. The results 

 are stated below very briefly. 



Pilocarpin and Atropin in one per cent, solution. (1.) 

 These agents are antagonistic in action. (2.) Pilocarpin 

 is a cardiac depressant; atropin an excitant; the former 

 lowers cardiac excitability ; the latter most decidedly 

 heightens it ; the former weakens the beat and tends to 

 arrest the heart in diastole, the latter calls into action the 

 resources of the heart quickly and fully. 



Carbonates of Soda and Potash in five per cent, solution. 

 These agents are antagonistic in action. Sodium carbonate 



