THE MECHANISTIC CONCEPTION OF LIFE ii 



into the egg. This membrane formation led only to a beginning but 

 not to a complete development. We may, therefore, conclude 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 butyric acid does; and secondly a sub- 

 stance which corresponds in its effect to the influence of the hypertonic 

 solution in the sea-urchin egg after the membrane formation. 



The question arises as to how the destruction of the cortical 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 oxygen; if the oxygen is completely withdrawn the development stops, 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 spermatozoon causes 

 the development by accelerating the oxidations in the egg. This con- 

 clusion was confirmed by experiments by 0. Warburg and by Wasteneys 

 and myself in which it was found that through the process of fertiliza- 

 tion 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 destruc- 

 tion 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. 



We, therefore, see that the process of the activation of the egg by the 

 spermatozoon, which twelve years ago was shrouded in complete dark- 

 ness, to-day is practically completely reduced to a physico-chemical 

 explanation. Considering the youth of experimental biology we have 

 a right to hope that what has been accomplished in this problem will 

 occur in rapid succession in those problems which to-day still appear 

 as riddles. 



5. Nature of Life and Death 



The nature of life and of death are questions which occupy the in- 

 terest of the layman to a greater extent than possibly any other purely 

 theoretical problem ; and we can well understand that humanity did not 

 wait for experimental biology to furnish an answer. The answer as- 

 sumed the anthropomorphic form characteristic of all explanations of 

 nature in the prescientific period. Life was assumed to begin with the 

 entrance of a " life principle " into the body ; that individual life be- 



