The Mechanistic Conception of Life 13 



egg. This membrane formation led only to a beginning but 

 not to a complete development. We may, therefore, con- 

 clude that the spermatozoon causes the development of the 

 egg in a way similar to that which takes place in the case of 

 artificial parthenogenesis. It carries first a substance into 

 the egg which destroys the cortical layer of the egg in the 

 same way as does butyric acid; and secondly a substance 

 which corresponds in its effect to the influence of the hyper- 

 tonic solution in the sea-urchin egg after the membrane 

 formation. 



The question arises as to how the destruction of the corti- 

 cal layer can cause the beginning of the development of the 

 egg. This question leads us to the process of oxidation. 

 Years ago I had found that the fertilized sea-urchin egg can 

 only develop in the presence of free oxygen; if the oxygen 

 is completely withdrawn the development stops, but begins 

 again promptly as soon as oxygen is again admitted. From 

 this and similar experiments I concluded that the spermato- 

 zoon causes the development by accelerating the oxidations 

 in the egg. This conclusion was confirmed by experiments 

 by O. Warburg and by Wasteneys and myself in which it was 

 found that through the process of fertilization the velocity 

 of oxidations in the egg is increased to four or six times its 

 original value. Warburg was able to show that the mere 

 causation of the membrane formation by the butyric acid 

 treatment has the same accelerating effect upon the oxidations 

 as fertilization. 



What remains unknown at present is the way in which 

 the destruction of the cortical layer of the egg accelerates the 

 oxidations. It is possible that the cortical layer acts like 

 a solid crust and thus prevents the oxygen from reaching 

 the surface of the egg or from penetrating into the latter 

 sufficiently rapidly. The solution of these problems must 

 be reserved for further investigation. 



