Puysr1oLogicaL Errects or Lack or OxyGen B81 
hour all of the control eggs had developed into the two-cell 
stage, but did not go any farther. When exposed to room 
temperature, an incomplete division occurred in a small 
number of the experimental eggs after thirty minutes. 
Only a suggestion of a membrane dividing the two cells 
was formed; the peripheral cell-membranes were not formed. 
The process then came to a standstill. That this result was 
attributable to the lack of oxygen, and not to the prolonged 
stay in the cold, was shown by the fact that when, after 
some time, the gas-chamber was opened, vigorous cleavage 
set in in all the eggs after thirty minutes. 
The experimental eggs in a third experiment remained on 
the ice for two hours. The control eggs reached the four- 
cell stage within the first eighty minutes. Cleavage then 
ceased. When the experimental eggs were taken from the 
ice, not a suggestion of cleavage set in during the following 
eighty minutes. Air was then admitted. All the eggs be- 
gan to divide in thirty minutes. 
I obtained the same result in more than ten further ex- 
periments. With the exception of the fact that in an occa- 
sional egg among hundreds an intimation of a dividing 
membrane was visible, no cleavage whatsoever occurred 
when a vigorous stream of hydrogen was led for two hours 
or longer before the beginning of the experiment through 
the gas-chamber which contained the experimental eggs and 
was kept on the ice. Yet the same eggs all divided within 
half an hour when later exposed to the air. 
It might be thought that lack of oxygen only markedly 
retards cleavage, but does not bring it to a complete stand- 
still. Yet it did not matter how long one waited—cleavage 
never occurred in the gas-chamber in the case of lack of 
oxygen, when all the oxygen had been driven out. 
Furthermore, I ascertained that when any segmentation 
whatsoever occurred in a weak stream of hydrogen, it always 
Digitized by Microsoft® 
