164 L. V. HEILBRUNN. 



that some of the "membrane-forming substances" cause the 

 egg membrane of the Mollusk Lottia to swell, but he admits 

 that this is not true of all of them. Some seem to cause swelling 

 and final liquefaction of the chorion or jelly of the sea-urchin 

 egg, but here again all are not effective, and I can suggest 

 chloroform as an exception. In fact it must be a strange colloid 

 which can be made to absorb water by such reagents as distilled 

 water, alcohol, chloroform, toluol, picric acid. 



2. It is difficult to conceive of the location of the swelling 

 colloid. The egg has been shown to consist essentially of a more 

 or less rigid membrane surrounding a mass of fluid contents. 

 Evidently the latter can not swell, as only gels possess this prop- 

 erty. It is also demonstrable that the outer vitelline membrane 

 itself does not swell in the case of true membrane elevation, 

 for it can scarcely be doubted that the vitelline membrane 

 undergoes an increase rather than a decrease of rigidity after 

 elevation. And swelling is always correlated with a decrease 

 in rigidity on the part of the gel. It is difficult to understand 

 how Loeb seeks to explain by swelling what he regards as the 

 formation of a more or less rigid membrane. 



3. Cytolysis results not in colloidal swelling and liquefaction, 

 but in coagulation. Loeb considers membrane elevation and 

 cytolysis as due to the same processes. He says: 1 "Substances 

 like benzol, saponin, etc., can cause both membrane formation 

 and cytolysis. The first of the two is produced when they 

 have time to affect only the surface of the egg; cytolysis is 

 produced when their effect extends to the deeper layers of the 

 egg . . . the greater the fraction of the egg which conies under 

 the effect of the membrane-forming reagents, the greater the 

 amount of colloid that must be liquefied." Loeb thus states 

 explicitly that the membrane-forming reagents "liquefy" the 

 colloids of the eggs, and that this effect in the case of cytolysis 

 extends into the interior. Now it is a fact that the membrane- 

 forming reagents, far from producing liquefaction, have an ex- 

 actly opposite effect upon the colloids of the Arbacia egg. 

 Instead of transforming a solid mass to a more fluid state, what 

 they really do is exert a solidifying or rather a coagulating effect 



1 Loc. cit., p. 213. 



