Membrane Formation and Cytolysis 185 



Then the egg becomes permeable for salts but not for colloids. 

 Then the sudden swelling in Fig. 58 takes place. We shall 

 return to this phenomenon in chap. xx. 



6. Increase of temperature also produces cytolysis. Dr. 

 von KnafH found that heating unfertilized sea-urchin eggs to 

 41° C. led to their practically instantaneous cytolysis. At 

 lower temperatures a longer time is necessary for cytolysis.^ 

 I found that by merely warming sea-urchin eggs to 34° or 35° C, 

 the formation of a typical fertilization membrane can often, 

 but not always, be induced.^ If the eggs are then cooled 

 quickly, no cjdiolysis follows. Such eggs are no longer capable 

 of development, since a temperature of 34° C. kills them. 

 But starfish eggs, which can also be caused to form membranes 

 by warming, can endure a higher temperature, and develop 

 under these conditions (according to experiments of Ralph S. 

 Lillie, which we shall discuss later). 



7. We will now return to a short discussion of the effect 

 of acids. We have already described in detail how the acids 

 cause membrane formation. As far as cytolysis of the sea- 

 urchin egg is concerned, I have obtained it only with the higher 

 fatty acids, beginning with heptylic, i.e., with heptylic, caprylic, 

 nonylic, and capric acids; this cytolysis is always preceded by 

 the formation of a fertilization membrane. The cytolysis 

 takes place while the eggs are in the solution. The experi- 

 ments were usually performed in N/500 or N/1,000 solution of 

 the acid, which was rendered isosmotic with sea-water by the 

 addition of some NaCl. Curiously enough, the addition of 

 some Ca promoted the membrane formation in a very marked 

 fashion. Oleic acid (rendered isotonic with sea-water by NaCl) 

 also caused membrane formation and cytolysis in the sea-urchin 

 egg. With the lower fatty acids, from capronic downward, I 

 have so far obtained membrane formation, but no rapid 



1 Von Knatfl, Pfiuger's Archiv, CXXIII, 279, 1908. 



2 Loeb, Pftager's Archiv, CXXII, 199, 1908. 



