XVII 
MEMBRANE FORMATION AND CYTOLYSIS 
1. In this chapter we shall show that all haemolytic agents 
also cause membrane formation. We find usually that a short 
exposure of the egg to such a reagent leads only to membrane 
formation, a longer one to cytolysis. According to Koéppe, 
besides electricity and heat, there are five classes of reagents 
that cause cytolysis; they are: (1) certain specific substances, 
such as glucosides (e.g., saponin) or bile_ salts; (2) a number v 
of fat-solvents, such as benzol, ether, and alcohol; (3) distilled V 
water; (4) acids; (5) bases. We have already seen that the 
two last-named substances lead to membrane formation, and 
we shall show that the same is true for the others, and that with 
proper after-treatment this membrane formation leads to the 
development in the sea-urchin egg (and the eggs of other 
forms). We can therefore say briefly that all haemolytic agencies 
effect the activation of the unfertilized egg, and this activation con- 
sists in a cytolysis of the cortical layer of the eggs. 
I first noticed the connection between membrane formation 
and cytolysis when in 1904 I was trying to discover why no 
typical membrane was formed in my original method of artificial 
parthenogenesis by hypertonic solutions. In the course of these 
investigations it happened that when the osmotic pressure was 
high enough, e.g., with 13 m solutions of NaCl or cane sugar, the 
unfertilized eggs produced a splendid fertilization membrane; 
but this membrane formation was followed almost at once by 
a cytolysis of the whole egg.'| A similar phenomenon occurs 
when the eggs are placed in distilled water; for they also form 
membranes and are immediately afterward transformed into 
“shadows.” 
1 Loeb, ‘“‘Ueber Befruchtung, kiinstliche Parthenogenese und Zytolyse des 
Seeigeleies,’’ Pfliiger’s Archiv, XCIII, 257, 1904; Untersuchungen, p. 288. 
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