198 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



While it was thus easy to cause the membrane formation of 

 the unfertilized sea-urchin egg with blood or extracts of tissues 

 from foreign species, it was almost impossible to bring about 

 the membrane formation in the sea-urchin egg with extracts 

 from the tissues of the sea-urchins. Only in one among many 

 attempts did the writer succeed in causing membrane formation 

 in the eggs of S. purpuratus by the watery extract from the 

 coecum of S. franciscanus. The extract had been standing five 

 days; newly prepared extract was without effect upon the same 

 eggs. About 5 per cent of the eggs formed membranes. 



We may ask the question why it is that blood or the extracts 

 of tissues of foreign species will readily cause membrane forma- 

 tion in the unfertilized eggs of sea-urchins, while the extract 

 from tissues of the sea-urchin remains ineffective. From the 

 experiments with acids and alkali it became evident that a 

 necessary prerequisite of the efficiency of a substance for the 

 causation of membrane formation is its diffusion into the egg, 

 or at least into its cortical layer. The same can be shown to 

 be true for the hydrocarbons, ether, alcohols, and the other 

 substances which cause membrane formation. It is therefore 

 possible that the inefficiency of the blood and tissue extracts 

 of the same animal and the efficiency of the blood of foreign 

 species for the causation of membrane formation is due to the 

 fact that the foreign lysins can diffuse into the egg while the 

 lysins of the same species cannot. 



We know that the blood of all animals carries lysins which 

 may cause haemolysis in foreign forms, but are harmless to 

 the cells of the animal itself. What causes this immunity ? 

 According to our investigations the immunity of our cells 

 against the lysins contained in our blood may be due to the 

 fact that the lysins of our blood cannot diffuse into our own 

 cells while they may diffuse into the cells of foreign species. 



This view is supported by some data which will be given in 

 the next chapter and to which we may refer briefly here. The 



