B74 STUDIES IN GENERAL PHYSIOLOGY 
without oxygen, we are inclined to imagine that the given 
organ or organism lacks the necessary energy for performing 
this function. If we remember, however, that the conver- 
sion of chemical into the physiological function depends 
upon definite molecular conditions in the cells (state of mat- 
ter, osmotic pressure, surface tension, phenomena of spread- 
ing, etc.), another explanation is possible, a priorz: the cells 
are still able to produce the energy necessary for the physio- 
logical functions of the organ, but lack of oxygen led to 
molecular changes in the cells which prevented the conver- 
sion of the chemical energy into mechanical or other forms 
of energy. So far as I know, there are as yet no facts at 
hand to support such a view. Yet the following experi- 
ments, I believe, have led to positive results in this direction, 
for we can show that the eggs of Ctenolabrus and sea-urchin 
cannot segment without oxygen, and that, moreover, the 
already formed cleavage-cells of these eggs, especially those 
of Ctenolabrus, undergo certain structural changes when 
deprived of oxygen, which cause the cells to fuse together. It 
is possible that in this case we deal with a liquefaction of the 
membrane or the specific surface film of the cleavage-cells, 
and furthermore that the impossibility of the formation of a 
membrane in the absence of oxgen is why no cleavage occurs 
under these conditions. But no matter what one may 
assume regarding the formation of a membrane, it is clear 
that when separate cells fuse in the absence of oxygen, it is 
not to be expected that the unsegmented egg will be able to 
divide under these conditions. But those cells which have 
fused are by no means dead. When they are again supplied 
with air, segmentation sets in anew. We therefore see that 
the structural changes resulting from the absence of oxygen 
suffice to explain the failure of segmentation, and that it is 
not necessary in this case to attribute the latter to a failure 
of the source of chemical energy. This conclusion is further 
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