416 STUDIES IN GENERAL PHYSIOLOGY 
Finally, it was of interest to compare the resuscitating 
effect of air with the resuscitating effect of hydrogen. Fun- 
dulus embryos were introduced into two gas-chambers. At 
the beginning of the experiment the heart under observation 
in one of the chambers beat 90 times a minute; that in the 
other, 96 times a minute. Hydrogen was passed through 
the chambers, and after an hour and fifty minutes the 
frequency of the heart-beats had fallen in both cases to 18 
per minute. In place of the hydrogen, carbon dioxide 
was then passed through the chambers. In fifteen minutes 
the ventricles stopped beating, and the pulsations of the 
auricles became much weaker. After 45 minutes one of the 
hearts was apparently dead, while the auricle of the other 
still beat 18 times a minute, though the beats were scarcely 
perceptible. One of the gas-chambers was then opened 
and the embryo exposed to the air, while in the second cham- 
ber the CO, was replaced by hydrogen. After fifteen 
minutes the heart which had been apparently dead and 
which was exposed to the hydrogen beat 24 times a minute, 
but only the auricles contracted. Both the auricle and the 
ventricle of the heart which was exposed to the air beat 
60 times. Two hours later the heart beat 30 times per 
minute in the hydrogen, but the contractions were still 
limited to the auricle, while the heart exposed to the air 
beat 72 times. When a little later I exposed the em- 
bryo kept in the hydrogen to air, the ventricle did not 
recover. The number of auricular contractions did rise 
within fifteen minutes from 18 to 54, but shortly there- 
after the entire heart ceased to beat. In resuscitating a 
heart poisoned by CO,, oxygen is therefore more effect- 
ive than the simple removal of the CO, by hydrogen. 
We are not able to explain why the ventricle ceases to 
beat when exposed to carbon dioxide sooner than the auricle. 
We meet with an entirely different relation between car- 
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