MEMBRANE FORMATION AND CyYTOLYSIS 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 Knaffl 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.2 If the eggs are then cooled 
quickly, no cytolysis foliows.. 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, | 
have so far obtained membrane formation, but no rapid 
1 Von Knaffl, Pfliiger’s Archiv, CX XIII, 279, 1908. 
2 Loeb, Pfliiger’s Archiv, CX XII, 199, 1908. 
