252 Influence of environment on animals 



some of the injurious effects of acid treatment. Thus the unfertilised 

 eggs of the sea-urchin Strongylocentrotus purpuratus of the Californian 

 coast begin to develop when membrane-formation has been induced 

 by treatment with a fatty acid, e.g. butyric acid ; but the develop- 

 ment soon ceases and the eggs perish in the early stages of segmen- 

 tation, or after the first nuclear division. But if we treat the same 

 eggs, after membrane-formation, for from 35 to 55 minutes (at 15 C.) 

 with sea-water the concentration (osmotic pressure) of which has 

 been raised through the addition of a definite amount of some salt or 

 sugar, the eggs will segment and develop normally, when transferred 

 back to normal sea- water. If care is taken, practically all the eggs 

 can be caused to develop into plutei, the majority of which may be 

 perfectly normal and may live as long as larvae produced from eggs 

 fertilised with sperm. 



It is obvious that the sea-urchin egg is injured in the process of 

 membrane-formation and that the subsequent treatment with a 

 hypertonic solution only acts as a remedy. The nature of this 

 injury became clear when it was discovered that all the agencies 

 which cause haemolysis, i.e. the destruction of the red blood 

 corpuscles, also cause membrane-formation in unfertilised eggs, e.g. 

 fatty acids or ether, alcohols or chloroform, etc., or saponin, solanin, 

 digitalin, bile salts and alkali. It thus happens that the phenomena 

 of artificial parthenogenesis are linked together with the phenomena 

 of haemolysis which at present play so important a role in the study 

 of immunity. The difference between cytolysis (or haemolysis) and 

 fertilisation seems to be this, that the latter is caused by a superficial 

 or slight cytolysis of the egg, while if the cytolytic agencies have 

 time to act on the whole egg the latter is completely destroyed. If 

 we put unfertilised eggs of a sea-urchin into sea- water which contains 

 a trace of saponin we notice that, after a few minutes, all the eggs 

 form the typical membrane of fertilisation. If the eggs are then 

 taken out of the saponin solution, freed from all traces of saponin 

 by repeated washing in normal sea-water, and transferred to the 

 hypertonic sea-water for from 35 to 55 minutes, they develop into 

 larvae. If, however, they are left in the sea-water containing the 

 saponin they undergo, a few minutes after membrane-formation, the 

 disintegration known in pathology as cytolysis. Membrane-formation 

 is, therefore, caused by a superficial or incomplete cytolysis. The 

 writer believes that the subsequent treatment of the egg with 

 hypertonic sea-water is needed only to overcome the destructive 

 effects of this partial cytolysis. The full reasons for this belief 

 cannot be given in a short essay. 



Many pathologists assume that haemolysis or cytolysis is due to 

 a liquefaction of certain fatty or fat- like compounds, the so-called 



