PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 381 



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 



