HEART BEAT OF FRESH WATER ANIMALS. 205 



The turtles used were mostly those common to this locality 

 (California), but a few were from Illinois — the Emys Meleagris. 



It may be as well to begin by stating that the turtle's heart 

 will remain alive as long in dilute sea water as in " Ringer." By 

 "alive" is meant that condition of the heart in which, though 

 quiescent it still responds to a stimulus by a contraction. Usually 

 an induction current was used to ascertain if the heart would still 

 contract. Individual hearts vary within such wide limits that in 

 experiments on the whole heart controls were considered of such 

 doubtful value that they were seldom used. The temperature 

 also is a factor, for in warm weather bacterial decomposition soon 

 sets in. In cool weather records of the ventricle have been 

 obtained extending over one hnndred hours ; but most of this 

 work was done at higher temperatures and the hearts would not 

 last as long either in sea water or in " Ringer." The auricles 

 have given an uninterrupted series of contractions lasting eighteen 

 hours or more, in cool weather. 



When a strip of ventricle from a turtle's heart is immersed in 

 isotonic sea water, it remains perfectly quiet indefinitely. Occa- 

 sionally it will give a single spontaneous contraction, but it has 

 been known to remain for twenty-four hours without giving a 

 single beat. The shortest time in any of my experiments that it 

 remained quiet was three hours and three quarters, when it gave 

 one contraction, followed by two more eighteen hours later. 

 Control strips in " Ringer" would invariably give single contrac- 

 tions or groups of contractions, separated by periods of quies- 

 cence, and were always more active than the corresponding strips 

 in sea water. If, however, the strips were first treated with pure 

 NaCl in m/8 concentration until "sodium chloride arrest" was 

 induced, the difference was more marked. The strip transferred 

 to " Ringer" usually recovered and gave a good series of con- 

 tractions ; while that transferred to sea water would revive for a 

 few minutes and then become quiet, giving contractions of a very 

 slow rate, or even none at all. That it was still capable of con- 

 traction was demonstrated by its response to stimulation with 

 the induced current. 



In striking contrast to the apical strips was the behavior of the 

 auricles, always taken from the same heart for comparison. As 



