NaturaL DEATH AND FERTILIZATION 747 
the egg. Such an acceleration might, for example, be 
brought about through certain ions (for example, the 
hydrogen ions of nucleic acid), yet the possibility that 
such catalytic effects might also be brought about through 
enzymes or other substances is of course not shut out. Yet 
this fact must be considered: that we have been able to 
produce artificially normal embryos capable of development 
through ions, while the careful experiments of Gies con- 
ducted in my laboratory, in which he attempted to find the 
same to hold for enzymes, have thus far failed. 
In conclusion I wish to thank my assistant, Mr. Neilson, 
for the assistance which he rendered me in these experi- 
ments. 
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