PHYSIOLOGICAL EFFICIENCY OF ACIDS 141 
formation does not occur after transference to normal sea-water 
if the eggs have been too long in the fatty acid solution. Why 
this should be so I cannot tell; possibly too much fatty acid 
enters the egg and the latter can no longer form a membrane. 
The following table gives a clear picture of this fact. The acid 
used was butyric. 
TABLE XXV 
PERCENTAGE OF Eaas Wuicnw ForMeED MEMBRANES AFTER EXPOSURE 
To Butyric Acip 
| | 4/500 N 
Length of Exposure to— N/500 2/500 N 3/500 N’ |Butyric Acid 
| lin m/2 NaCl 
| 
MSITIERNUT GOS ercieetsioree os 6<1s-- 100% 100% 100% 100% 
PATIMIMNUES See e-cieie-isicuss-> * = 100 100 10 10 
SSMIMITINUNGE SR aa slerelele < @ sos. 100 1 0 0 
PBVTRTANIGES Ses et oie a/s..etoce! =| se 80s 3 0 0) 
5) MOI no oko OOOO Ee | note 0 0 0 
It can be seen from this table that unfertilized sea-urchin 
eggs can no longer form membranes if they remain longer 
than two minutes in a 3/500 N solution of butyric acid (in 4 m 
NaCl solution). If sperm now be added to such eggs after they 
are transferred to normal sea-water, no egg is fertilized and none 
develops. I thought at first that it depended upon a reversible 
acid effect and that the eggs would be able to recover after a 
long stay in sea-water. But that is not the case. As a control, 
the eggs of the same female were then placed in a N/50 solution 
of HCl, in which they remained four minutes. Not one formed 
a membrane after transference to normal sea-water. But 
upon the addition of sperm 40 per cent of these eggs were ferti- 
lized and developed in a perfectly normal fashion. We have 
seen that benzoic acid is much better for causmg membrane 
formation than butyric acid. We should expect that it is 
correspondingly more injurious. This is also the case. Eggs 
were placed in a N/500 benzoic acid solution. Every minute 
some of the eggs were transferred to normal sea-water. The 
