422 STUDIES IN GENERAL PHYSIOLOGY 



through lack of oxygen, which in their turn are the cause 

 of the suspension of life-phenomena. This has been proved 

 for the process of cleavage in the Ctenolabrus egg. The 

 cleavage-cells of Ctenolabrus are dissolved again and fuse 

 together when oxygen is removed. These changes are not, 

 however, an evidence of death, for as soon as such a fused 

 blastoderm is again exposed to air it begins to divide anew. 

 On the other hand, these molecular changes are sufficient to 

 hinder cleavage. The cleavage-cells of the Arbacia egg 

 seem to suffer similarly in the lack of oxygen, although the 

 changes are much less marked. We find that here also 

 cleavage is impossible without oxygen. Yet lack of oxygen 

 does not bring about the same sort of molecular changes in 

 the Fundulus egg as in the Ctenolabrus egg, and corre- 

 sponding with this difference cleavage may also go on with- 

 out oxygen for many hours in Fundulus. 



It is also possible that such molecular changes as are 

 brought about by the lack of oxygen in the cell are also the 

 cause of the cessation of other life-phenomena; for example, 

 the beat of the heart (and the activity of the respiratory 

 center). We thus find that in Ctenolabrus, where the first 

 cleavage-cells suffer such profound structural changes 

 through lack of oxygen, the heart of the embryo comes to a 

 standstill very rapidly and suddenly through lack of oxygen 

 before a marked decrease has taken place in the frequency 

 of the heart-beats; while the heart of the Fundulus, whose 

 cells suffer no such structural changes, continues to beat for 

 many hours without oxygen. Since the chemical energy 

 set free in the cells must first be converted into molecular 

 energy in order to bring about the physiological function, it 

 is clear, a priori, that not only a decrease in. the supply of 

 the chemical energy, but any structural change which ren- 

 ders impossible the conversion of chemical energy into the 

 molecular energy necessary for the activity of the tissue, 



