8 The Mechanistic Conception of Life 



these experiments the action of the spermatozoon upon the 

 egg was very incompletely imitated. When a spermatozoon 

 enters into the egg it causes primarily a change in the surface 

 of the egg which results in the formation of the so-called 

 membrane of fertilization. This phenomenon of membrane 

 formation which had always been considered as a phenomenon 

 of minor importance did not occur in my original method of 

 treating the egg with hypertonic sea-water. Six years ago 

 while experimenting on the Californian sea-urchin, Strongylo- 

 centrotus purpuratus, I succeeded in finding a method of 

 causing the unfertilized egg to form a membrane without 

 injuring the egg. This method consists in treating the eggs 

 for from one to two minutes with sea-water to which a definite 

 amount of butyric acid (or some other monobasic fatty acid) 

 has been added. If after that time the eggs are brought back 

 into normal sea-water, all form a fertilization membrane in 

 exactly the same way as if a spermatozoon had entered. 

 This membrane formation or rather the modification of the 

 surface of the egg which underlies the membrane formation 

 starts the development. It does not allow it, however, to 

 proceed very far at room temperature. In order to allow 

 the development to go farther it is necessary to submit the 

 eggs after the butyric acid treatment to a second operation. 

 Here we have a choice between two methods. We can 

 either put the eggs for about one half-hour into a h}' pertonic 

 solution (which contains free oxygen) ; or we can put them for 

 about three hours into sea-water deprived of oxygen. If the 

 eggs are then returned to normal sea- water containing oxygen 

 they all develop; and in a large number the development is as 

 normal as if a spermatozoon had entered. 



The essential feature is therefore the fact that the develop- 

 ment is caused by two different treatments of the egg; and 

 that of these the treatment resulting in the formation of 

 the membrane is the more important one. This is proved 



