THE FERTILISATION OF THE EGG 173 



suggested the possibility of a more perfect imitation of the 



natural process. Inquiry was next directed by Loeb to artificial 



membrane formation. In earlier experiments on the action 



of the hydrogen-ion, mineral acids were used. It was now 



found that exposure to ethyl acetate induced the production 



of a typical fertilisation membrane ; and further study showed 



that this action was due to the acid hydrolysis product. This 



suggested that the fatty acids might be successful agents of 



membrane formation. By leaving the unfertilised eggs of 



Strongylocentrotus in a mixture of 50 c.c. sea water and 2'8 



N 

 c.c. — butyric acid at 15° C. for about two minutes, all the 



eggs are induced to form membranes, when replaced in normal 

 sea water. Eggs of Strongylocentrotus subjected to this 

 treatment passed through the early developmental stages. 



The combination of both methods was next employed. 

 Exposure to the action of the fatty acid after treatment with 

 hypertonic sea water gave better results. When, however, 

 the reverse procedure was adopted, the eggs being treated 

 with hypertonic sea water (for a shorter period) after artificial 

 membrane-formation, success was complete. A hundred 

 per cent, yield of swimming larvae was obtained ; the larvae 

 were normal in their behaviour ; and the cleavage process 

 precisely resembled that of the normally-fertilised egg. Loeb 

 (1904-5) thus made what must be regarded as one of the most 

 audacious contributions to mechanistic thought in replacing 

 that mysterious complex the living sperm by familiar physico- 

 chemical agencies in its role of activating the developmental 

 process. 



Before pursuing the problem further, it will be as well 

 to form a more concrete picture of the ground so far traversed. 

 MacLendon (19 12) has shown that fertilised eggs readily 

 shrink in isotonic sugar solutions ; but that the unfertilised 

 eggs do not do so with equal readiness. From this and other 

 experiments by MacLendon and by Gray on the conductivity 

 of the egg before and after fertilisation there seems good reason 

 to believe that an essential feature of normal fertilisation is 

 increased permeability of the cell-membrane. A variety 



