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 EGGS WHICH FORMED MEMBRANES AFTER EXPOSURE 



TO BUTYRIC ACID 



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 J 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 HC1, 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 causing 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 



