130 The Mechanistic Conception of Life 



and 2 (page 7) show these changes m the sea-urchin egg. Fig. 

 1 represents the unfertilized egg, Fig. 2 shows the same egg 

 after the entrance of the spermatozoon. 



In 1905 I succeeded in finding a method by which it is 

 possible to call forth the formation of a membrane of fertiliza- 

 tion without apparent injury to the egg. This method consists 

 in putting the eggs for about two minutes (at a temperature 

 of 15°) into a mixture of 50 c.c. of sea-water-f3 c.c. of an n/10 

 lower monobasic fatty acid, e.g., acetic, propionic, butyric, or 

 valerianic acid. In this mixture no membrane formation 

 takes place; if, however, the eggs are transferred into normal 

 sea-water all the eggs form a perfect fertilization membrane. 

 The experiments showed that this process of membrane forma- 

 tion is the essential condition which causes the egg to develop. 

 In all these eggs in the course of the next hours after the mem- 

 brane formation those changes begin which lead to a cell- 

 division. If the temperature is very low not only cell-divisions 

 begin but the egg may develop into a swimming larva; it 

 reaches the so-called blastula stage. At room temperature, 

 however, the artificial production of a membrane in the egg 

 by fatty acid only calls forth a nuclear and possibly a cell- 

 division; after this the egg slowly begins to disintegrate. 



We therefore see that the artificial membrane formation 

 by a fatty acid induces the developmental process, but that 

 at ordinary temperature the latter does not go far. In order 

 to cause a complete development, a second influence is needed, 

 as we shall see later. 



Before we describe this second influence, another question 

 has to be settled, namely, how we know that the membrane 

 formation and not any other action of the acid, e.g., a catalytic, 

 is the formative stimulus in this case. The answer is, that if 

 we apply the acid but prevent the changes leading to a mem- 

 brane formation, divisions of the nucleus and of the cell do not 

 occur. On the other hand, we shall see later on that we can 



