174 L - V - HEILBRUNN. 



substances which increase the modulus of elasticity. 1 As a result 

 of the stiffening action of KCN, the membrane resists elevation, 

 for the elevating force is not sufficient to stretch it. But in a 

 hypertonic solution, as the egg shrinks, no stretching is necessary 

 to separate the vitelline membrane from the egg, and the mem- 

 brane is accordingly pulled away from the egg surface. 



E. Inhibitors to Membrane Swelling. 



It has been found that swelling of the vitelline membrane 

 may be retarded or even inhibited in the presence of certain 

 substances. Up to the present only two such inhibiting sub- 

 stances have been discovered. Of these, KCN inhibits the 

 swelling of the membrane by salts, sea-urchin blood on the other 

 hand inhibits acid swelling. But the inhibitor of salt action 

 has no such effect on acid swelling, and sea-urchin blood in- 

 stead of inhibiting swelling produced by salts, actually seems 

 to favor it. These results, paradoxical as they appear at first 

 sight, are really in direct line with recent findings in the field of 

 colloid chemistry. There it has been shown that the salt and 

 the acid swellings of gelatine must be essentially different 

 processes, for the very salts which, by themselves, favor or even 

 cause swelling, retard the swelling effect of an acid. 



Although membrane swelling usually occurs in "NaCl hyper- 

 tonic sea-water," 2 in the presence of traces of KCN no such 

 swelling will occur. This inhibiting effect of KCN has as yet 

 not been found to be shared by any other substance, but so far 

 only a few experiments in this direction have been made. Some 

 of the experiments made during the summers of 1913 and 1914 

 are recorded below. 



August 29, 1913. To 200 c.c. of sea-water was added 32 c.c. 

 of 2.5 M NaCl and the resultant "NaCl hypertonic sea-water" 

 was divided into four 50 c.c. portions, A, B, C, D. To A was 

 added 0.5 c.c. I per cent. KCN, to B 0.5 c.c. N/io NaOH, to 

 C, 0.5 c.c. ether, and nothing was added to D, which several 

 as a control. 



Eggs were then placed in A, B, C, D, and it was found that 

 although membrane swelling very evidently took place in D, 



1 Freundlich, "Kapillarchemie." p. 512. 



2 As previously stated, I use this term to indicate a solution of 50 parts (by 

 volume) of sea-water plus 8 parts of z\ M NaCl. 



