HEART BEAT OF FRESH WATER ANIMALS. 207 



quiet for eleven hours. It was then stimulated with the induced 

 current, and gave five vigorous contractions of maximum ampli- 

 tude after which it was again quiescent. Twenty-two hours after 

 beginning the experiment, it was again stimulated and gave a 

 fairly good contraction of about one third the maximum in height. 

 The solution was turbid indicating bacteria, and two hours later 

 it failed to respond to stimulation. The auricle of this heart was 

 placed in " Ringer " and gave a fine series of contractions lasting 

 eleven and one half hours, with an initial rate of twenty, which 

 was increased to twenty-four after immersion in " Ringer." 



Exp. Feb. 4/'o7 ; temperature i8° C. Two strips of the 

 turtle's heart were prepared as usual. Both strips were put in 

 m/8 NaCl in order to bring them to " sodium chloride arrest." 

 Strip A began contracting after a latent period of fifteen minutes ; 

 its rate, five per minute, increasing to fifteen with gradually dimin- 

 ishing amplitude. At the end of two hours and fifteen minutes 

 it ceased contracting. After remaining quiet for fifteen minutes 

 it was transferred to " Ringer." It began at once to recover, but 

 the contractions were small in amplitude, accompanied by a 

 strong rise of tone. The rate was nine, increasing to fifteen per 

 minute. Nine and one half hours from beginning the experi- 

 ment, it responded to electrical stimulation by a very feeble 

 twitch. Strip B began contracting after a latent period of fifteen 

 minutes. Its rate was four per minute increasing to twelve. It 

 came to "sodium chloride arrest" at the same time as did strip 

 A, and was transferred to dilute sea water. It began contracting 

 at once with a rate of nine per minute. After about fifteen min- 

 utes it ceased suddenly for five minutes and then began centract- 

 ing feebly and in groups. It then settled down to a slow rate 

 ■of one or two per minute, but with increased amplitude, and con- 

 tinued this for four and one half hours. It was stimulated with 

 the induced current at the same time as was strip A, and gave 

 a single contraction that was more vigorous than strip A, although 

 it was still feeble. The auricle was contracting in the air at a 

 rate of twenty per minute. After it was put in sea water the rate 

 was twenty-four. It gave an uninterrupted series of contractions 

 lasting about nine hours. After a long rest it recovered a little 

 and gave some weak contractions. The duration of its irritabil- 



