414 STUDIES IN GENERAL PHYSIOLOGY 



oxygen supply and at the same temperature. When, how- 

 ever, we consider the results of the experiments carried on 

 in the cold, we come to the conclusion that in the presence of 

 oxygen the proportion of energy obtained through processes 

 of splitting may be much greater than this; it may then 

 amount to 50 or 70 per cent, of the work done by the heart. 

 The behavior of the heart of a Fundulus embryo in car- 

 bon dioxide is of interest in so far as it shows that carbon 

 dioxide is just as poisonous in this case as upon the heart of 

 the Ctenolabrus. While the Fundulus heart continues to 

 beat for twelve hours, and even longer, when the oxygen is 

 driven out by hydrogen, the ventricle ceases to beat as early 

 as twelve minutes after passing carbon dioxide through the 

 gas-chamber. Only the auricle continues to beat, and the 

 circulation soon comes to a stop. The contractions become 

 weaker and less numerous. In one experiment the heart 

 beat 96 times per minute at the beginning of the experiment, 

 54 times after eight minutes, 45 times after ten minutes, 

 and 42 times after twenty minutes. The heart then ceased 

 to beat entirely for long periods of time, and thirty-two 

 minutes after turning on the carbon dioxide the heart 

 stood still. In other experiments the heart did not cease 

 to beat until after one and one-half hours. When the 

 heart is exposed to the poisonous effect of CO 2 and ceases 

 to beat even after one hour, the heart begins to beat 

 again when the carbon dioxide is replaced by air. The 

 resuscitation of the heart is as follows: The auricle recovers 

 more rapidly than the ventricle, and the latter at first beats 

 a less number of times than the former. In one ex- 

 periment a heart which had come to a standstill was exposed 

 to air at 10 A. M. At 10:06 the auricle beat 24 times per 

 minute, while the ventricle was still quiet. The ventricle 

 did not begin to contract until the next minute, and the 

 number of auricular contractions was 33 a minute at this 



