412 STUDIES IN GENERAL PHYSIOLOGY 
3:05 - 75 beats per minute 
3:08 - SB ae ss 
3:15 Ba ee et of 
8:25 96 oc 6c “ 
3:35 102 “ * 6 
3:47 i his ee sf 
3:53 120% ™ - 
This rate continued until 5:10, when it increased to 132.' 
This experiment, which I repeated several times with the 
same result, shows that the decrease in the number of heart- 
beats when the heart is deprived of oxygen is dependent 
chiefly upon the decrease in the energy furnished by oxida- 
tion and not upon the formation of poisonous substances. 
The fact that the minimum number of heart-beats continues 
a very long time without oxygen also speaks against the 
latter idea. 
We can make use of still another method to determine 
what proportion of the heart-beats in the Fundulus embryo 
depends upon oxidations, and what proportion upon pro- 
cesses of splitting. By placing the gas-chamber upon ice 
and passing a current of hydrogen through it, we are able to 
drive out the oxygen, while the processes of hydrolysis are 
at the same time reduced to a minimum through the lower- 
ing of the temperature. In one experiment I passed the 
hydrogen through the gas-chamber for two hours, while 
keeping it on ice. The hearts were then removed from the 
ice, but the current of hydrogen was maintained. At room 
temperature the number of heart-beats, which at the begin- 
ning of the experiment had been 117, rose to 87 (in 
twelve minutes), to descend again to 36 in the course of 
the next hour. Forty minutes later the minimum of 21 
was attained, at which rate the heart continued to beat 
for seven hours. Toward the last a slight increase occurred 
1 This experiment shows that the oxygen diffuses comparatively rapidly into the 
egg. [1903] 
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