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 eft'ect 

 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. 



