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 Engelmann 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 
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