PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 377 



different, however, when the function which we are study- 

 ing does not cease immediately. We are then unable to 

 say whether the transitory persistence of the function shows 

 that not all of the oxygen has been driven out, or that 

 the given function is not directly dependent upon oxygen. 

 Things of this sort confront us when we attempt to decide 

 whether cleavage is possible without oxygen. We find 

 that when sea-urchin eggs are placed in an Engelmann 

 chamber immediately after fertilization, and we begin to 

 pass hydrogen through it, the eggs not only cleave into 

 two, but often even into four, cells ; but this cleavage occurs 

 within the first fifty or eighty minutes after fertilization, and 

 it might be thought that it takes a longer time than this to 

 drive out all the oxygen. To be certain on this point in 

 such cases, I made use of the following procedure: I in- 

 troduced the eggs in which I wished to study the depend- 

 ence of cleavage upon oxygen into an Engelmann chamber 

 which was kept on ice. Hydrogen was then passed through 

 the apparatus. The low temperature inhibits cleavage. In 

 order to discover when I could take the eggs off the ice, and 

 know that the objection could no longer be raised that the 

 eggs still contain oxygen, I introduced a second gas-chamber 

 into the circuit. This contained eggs of the same culture, 

 and through it I passed the same current of gas as that 

 which went through the first. The second, control, chamber 

 was not put on ice. As long as a trace of cleavage continued 

 in this control chamber, there was reason to suspect that not 

 all the oxygen was driven out. As soon, however, as cleavage 

 ceased, it seemed reasonable to assume that, even though not 

 all the oxygen had been driven out of this chamber, the por- 

 tion which remained behind was no longer sufficient to start 

 cleavage. It must be remembered, however, that the eggs 

 kept on ice had not lost as much oxygen as the control eggs 

 during this time, for oxidation did not occur as rapidly in the 



