PRESERVATION OF THE LIFE OF THE EGG 289 
mature egg, while fertilization, which makes the egg immortal, 
raises the rate of oxidations considerably, at least in the egg 
of the sea-urchin. We have seen that in the unfertilized egg of 
the sea-urchin oxidations take place though at a slow rate. 
The unfertilized eggs seem to perish very rapidly through 
these oxidations. We have stated that the mature unfertilized 
egg resembles an anaerobe, while the act of fertilization trans- 
forms it into an aerobe. We are certainly here confronted 
with one of the most interesting and far-reaching features of 
the problem of fertilization. The unfertilized egg is perhaps 
at present the only instance of a cell for which ‘natural death” 
can be proven. The act of fertilization or rather the induce- 
ment of development procures theoretical immortality for the 
egg, since the sex cells of the new individual to which the egg 
gives rise are parts of the egg. 
The oxidations are, however, not the only processes which 
are responsible for the premature “natural death’ of the 
unfertilized egg; otherwise it should be possible to keep it 
alive indefinitely without oxygen, which is not the case. The 
act of fertilization brings about a profound physicochemical 
modification in the egg which is not confined to one type of 
chemical reactions. 
