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- 
mnent 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, eg. 
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 
