408 STUDIES IN GENERAL PHYSIOLOGY 
of droplets hinders the production or the transmission of 
molecular movements, and in this way brings about the sud- 
den standstill of the heart? This idea would also harmonize 
very well with the fact that the heart comes to a standstill as 
suddenly and as unexpectedly as death ensues from embol- 
ism. It would also be in harmony with this idea that after 
the sudden standstill of the heart a few occasional heart- 
beats may yet appear. We will, however, not enter farther 
into the field of hypotheses, but rather attempt to see how 
the heart of Fundulus behaves in the lack of oxygen. 
Numerous experiments on embryos from four to ten days 
old (the embryos do not hatch until after the twelfth day) 
showed without exception the following behavior of the heart 
in the case of lack of oxygen: 
During the first ten to twenty minutes after the hydrogen 
is turned on through the gas-chamber, the number of heart- 
beats does not decrease. A transitory acceleration even 
occurred, which, however, was brought about through a rise 
in temperature caused by passing the hydrogen gas through 
the gas-chamber. This acceleration did not occur when I 
packed the hydrogen generator in ice. But the decrease in 
the amount of oxygen contained in the Fundulus egg, which 
occurs during the first twenty minutes and which causes the 
heart of the Ctenolabrus embryo to stand still, has no effect 
upon the rate of the heart of the Fundulus embryo. 
Then follows a period of steady decrease in the number of 
heart-beats, which continues for about one and one-half 
hours. The decrease occurred most rapidly at first and then 
more slowly. During this period the number of heart-beats 
fell from about 120 or 100 a minute to about 20 per minute. 
This period corresponds, it seems to me (and we shall find 
further proofs for this idea later), to the period of progres- 
sive decrease in the oxygen necessary for the oxidations in 
the heart. 
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