378 STUDIES IN GENERAL PHYSIOLOGY 



former as in the control eggs. It was therefore necessary, 

 after cleavage had ceased in the control eggs, to pour the 

 current of hydrogen through the Engelmaiin chamber for 

 some time before the eggs to be experimented upon were 

 removed from the ice, and the real experiment was begun. 

 The objection might be raised that the prevention of 

 cleavage through the ice injured the eggs. I guarded 

 against this objection by the following control experiments: 

 First of all the eggs were again exposed to the air after the 

 completion of the experiment, and their cleavage observed. 

 If this took place in a normal way, its absence in the lack 

 of oxygen could not have been the effect of the cooling. 

 Secondly, another portion of the eggs of the same cul- 

 ture were put upon the ice at the same time and for the 

 same length of time as the eggs used in the experiment, 

 only they remained exposed to the air. I will state at once 

 that these eggs always segmented when brought back to 

 room temperature. During the entire time of the experi- 

 ment hydrogen passed uninterruptedly through the Engel- 

 mann chamber, not only to guard against possible leaks in 

 the apparatus, but also to remove the carbon dioxide formed. 

 The latter is absolutely necessary. 



III. RESEGMENTATION OF THE CTENOLABRUS EGG WITHOUT 



OXYGEN 



The older experiments of Spallanzani, Dutrochet, Saus- 

 sure, and Schwann had already established the fact that in 

 permanent lack of oxygen the development of plants and of 

 animal eggs is impossible. Paul Bert added to these ob- 

 servations the fact that when the air contains only 3.4 per 

 cent, of oxygen certain plants cease to germinate. In these 

 experiments, however, the question as to whether cell- 

 division is at all possible without oxygen was not touched 

 upon. Three years ago I began experiments on the eggs of 



