MECHANISM OF MEMBRANE FORMATION 215 
Robertson states that this order of inhibiting efficiency of 
various proteins is the reverse of their ability to pass through 
a porcelain filter. 
In striking confirmation of the view expressed by Loeb that the 
formation of the membrane in fertilized eggs is due to the osmotic 
imbibition of water by the egg, and that the inhibiting effect of colloids 
upon their formation is due to their inability to pass through the mem- 
brane, we find that the order of effectiveness of the various proteins 
in inhibiting membrane formation is the reverse order of their ability 
to pass through a porcelain filter. 
8. Membrane formation by acids or saponin or benzol is 
not dependent upon the presence of free oxygen. As I showed 
seven years ago, an egg is not deterred by KCN from forming 
a membrane under the influence of acid. I left unfertilized 
sea-urchin eggs at 15° C. for several hours (up to 24 hours) in a 
mixture of 50 c.c. of sea-water+2 c.c. 1/20 per cent KCN and 
added sperm thereto. The eggs at once formed perfect fertili- 
zation membranes in the cyanide sea-water.! But the develop- 
ment of the eggs was completely inhibited by such a solution. 
The development of the eggs requires free oxygen, but mem- 
brane formation by fatty acid, on the other hand, does not. 
In the case of artificial parthenogenesis by bases, however, 
oxidation is required for membrane formation. It is possible 
that in this case the process of oxidation leads to the formation 
of a substance which causes the physical change underlying 
membrane formation. 
9. What has the membrane formation to do with the 
development? The writer published in 1905 the following 
hypothesis: 
From ali these facts mentioned here, I have gathered the impres- 
sion that the membrane formation, or possibly the process which results 
in membrane formation, is an essential feature of the process of fertiliza- 
tion not only in the sea-urchin egg but also in at least certain starfish 
1Loeb, ‘‘Der chemische Charakter des Befruchtungsvorganges,” Biochem 
Zeitschr., L, 191, 1906. 
