PHYSIOLOGICAL EFFICIENCY OF ACIDS 145 
Why is it that, though the strong mineral acids do occasion- 
ally work, as a rule they fail? It has already been mentioned 
that if they produce any effect, membrane formation does 
not set in while the eggs are in the acid solution, but only after 
they have been transferred to normal sea-water. It is possible 
that the mineral acids only cause membrane formation indi- 
rectly, their immediate effect being to liberate from its salts 
some fatty acid contained in the surface of the egg, and that 
then the fatty acid thus liberated instigates membrane forma- 
tion. This hypothesis is supported by the following obser- 
vation. If 2 or 3 c.c: of N/10 HCl are added to 50 c.c. of 
sea-water, and unfertilized eggs placed in this solution, no 
membranes are as a rule formed by the eggs after transference 
to normal sea-water. A similar result is obtained if, instead of 
HCl, 2 or 3 c.c. of N/2 sodium butyrate are added to the sea- 
water. But if both HCl and sodium butyrate are added simul- 
taneously to the sea-water, the eggs do form a membrane 
when transferred from this to normal sea-water. In this case 
butyric acid is produced and diffuses into the egg. And there 
is no reason for supposing that a similar reaction may not take 
place when HCl comes into contact with the surface of the egg; 
for it might liberate here one of the higher fatty acids contained 
in combination in the surface of the egg. 
It may also be mentioned that the addition of a slightly 
effective minera! acid, such as HCl, to butyric acid does not 
influence the activity of the latter. I have performed many 
experiments of the kind, to see how far HCl can replace the 
fatty acid. It appears that HCi can only enter as substitute 
for a small amount of the fatty acid; perhaps some acid is 
combined with the proteins of the egg (especially of the chorion), 
and only this amount of fatty acid can be replaced by HCl. 
If more is added, everything proceeds as though the fatty acid 
concerned were in solution alone. The cnly effect of the sur- 
plus of H ions is that the confluence of the drops in membrane 
