PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 383 



when all the exhaustible oxygen has been removed so that 

 cell-division is no longer possible. The energy necessary 

 for these changes must probably therefore be obtained from 

 processes of hydrolysis. 



One might be tempted to believe that the nucleus could 

 continue to divide without oxygen, while the cell remains 

 undivided a phenomenon I discovered in sea-urchin eggs, 

 when they are brought into sea-water of a certain concentra- 

 tion. In such eggs the number of nuclei steadily increases, 

 but no cell-division occurs. But such phenomena certainly 

 do not take place in the absence of oxygen. Eggs were 

 freed from oxygen by passing hydrogen over them for two 

 hours while on ice. They were then exposed for one hour 

 to room temperature, while the flow of hydrogen was not 

 interrupted. No cleavage had occurred. The eggs were 

 then killed and sectioned. It was impossible to find more 

 than one nucleus in these eggs; this was, however, in a 

 number of instances undergoing mitosis. The experiment 

 was repeated with the same result. One mitotic division 

 may therefore occur without oxygen, but no more. 



If eggs which have been freed from oxygen for a suffi- 

 ciently long time while on ice, and which have shown no 

 evidence of cell-division when exposed to hydrogen for an 

 hour at room temperature, are exposed to the air, they all 

 divide in the course of thirty to fifty minutes. But they do 

 not then first divide into two cells and later into four, but 

 immediately into four occasionally into three or five cells. 

 This also occurs when a strong stream of hydrogen is sent 

 through the gas-chamber for three and a half hours at a low 

 temperature before the experiment is begun under condi- 

 tions therefore when, in all probability, all of the free oxygen 

 has been removed from the eggs. Two divisions of the 

 nucleus therefore always occur one in the hydrogen, and 

 one after the admission of air before the first cell-division 



