Meinhraiie Formation 



359 



TIME OF EXPOSURE 



TEMPERA- 



ture 



OPTIMUM CONC. OF ACID 



, • hi" 



I ■'. minutes < 



1 33 



/ ^3° 

 ■; minutes ^ 



I 33 



6 minutes n 



I 33 



6 cc. ^^ acid to 50 cc. s. w. 

 2-3 cc. i^- acid to 50 cc. s. w. 

 3-4 cc. ~ acid to 50 cc. s. w. 

 i4-2cc. ^ acid to 50 cc. s. w. 

 3 cc. J^ acid to 50 cc. s. w. 

 iw cc. ^^- acid to 50 cc. s. w. 



Both the optimum-time and optimum-concentration hgures 

 show a large increase in the efficiency of acetic acid with a rise of 

 temperature of io° C. Expressed m terms of a temperature- 

 coefficient (Q)io the mcrease amounts to a doubling, thus: 



Qio= ^ -2 



-'^ t + 10 



in which Q^y, is the ratio of a constant at a temperature t degrees, 

 to a constant at ^ -h io° C. The very marked efficiency at 36° 

 may be an additive effect as high temperatures are known to 

 cause membrane formation in both sea-urchins and starfish eoas. 

 I did not succeed in producing membranes on Toxopneustes eggs 

 by exposure to sea-water at those temperatures and for the times 

 used with the acid treatment. 



What changes might the dilute acetic acid bring about in the 

 ege; of a sea-urchin which would result in the formation of a mem- 

 brane.^ The chief possibihties are three. It might: 



1 Dissolve out the lipoids at the periphery. 



2 Change the surface tension of the egg directly, in that the 

 composition of the medium about the egg is altered. Instead of 

 egg protoplasm — sea-water, we have egg protoplasm — acid sea- 

 water. 



3 Combine with some of the egg proteids. 

 The first possibility has already been discussed. 



The surface tension between two phases is only very slightly 

 influenced by temperature. For the same reason diffusion rate 

 and degree of dissociation of CH3COOH would be negligible 

 factors. 



