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MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. X, NO. 3. 



The force of the objections to even the best form of the Williams apparatus was not 

 appreciated by us until we had made a number of experiments upon the isolated heart of the 

 frog. The record of those experiments which we made with the second form of the Williams 

 apparatus are as follows: 



Experiment 19. 



Experiment 20. 



Experiment 21. 



