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, 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 airat 104. 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 
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