MEMBRANE-FORMING AGENTS 461 



egg and the other, which is also brought about by the spermatozoon 

 and may be imitated by treating the eggs with hypertonic sea-water. 

 In the first place, as regards the cytolytic effect, or Membrane-formation 

 it has been found that the characteristic acceleration of Oxidations 

 which is induced by complete fertilization is also induced by membrane- 

 formation. Thus Warburg compared the rate of oxidations in unfer- 

 tilized eggs and in eggs which had been fertilized by sperm, and he 

 found that the consumption of oxygen in the eggs which had been 

 fertilized was 10.5 times the consumption of oxygen in the unfertilized 

 eggs. The same eggs after butyric acid treatment consumed 9.0 times 

 as much oxygen as the unfertilized eggs; the effect of membrane- 

 formation alone upon the basal metabolism was therefore very nearly 

 equal to that of complete fertilization. These experiments were re- 

 peated by Loeb and Wasteneys who, in another species of sea-urchin, 

 found the ratio of oxygen-consumption in unfertilized and sperm- 

 fertilized eggs to be 1 : 4.55, while two estimations of oxygen-consump- 

 tion in the same unfertilized eggs after membrane-formation by 

 butyric acid gave the values 1 : 4.72 and 1 : 4.28, indicating that the 

 effect of membrane-formation is to raise the rate of oxidations to 

 approximately the same height as the entrance of a spermatozoon. 



We have seen that membrane-formation is essentially a partial and 

 arrested Cytolysis. That this is really the essential feature in the proc- 

 ess and not merely an incidental phenomenon is shown by the fact 

 that if cytolysis be pushed even further, by whatever agent it may be 

 caused, the effect is to increase the consumption of oxygen by the egg 

 and approximately in proportion to the degree of cytolysis which is 

 induced. Cojnplete cytolysis of the egg of the sea-urchin can be caused 

 by the addition of Saponin to the sea-water. Loeb and Wasteneys 

 measured the rate of oxidations in a batch of unfertilized eggs in sea- 

 water and they found. that they consumed 0.15 mg. of oxygen per hour 

 at 15 C. The eggs were then cytolyzed with saponin and the amount 

 of oxygen consumed per hour at 15 C. determined again. It was 

 found to be 1.07 mg. The complete cytolysis of the eggs, therefore, 

 increased the rate of oxidation 700 per cent., or rather more than 

 fertilization itself. Cytolysis by hypotonic sea-water also causes an 

 increase in oxidations. 



The second factor in artificial fertilization, the treatment with Hyper- 

 tonic Sea-water, also increases the consumption of oxygen by the egg, 

 but only to a relatively slight degree, and not at all if it succeeds mem- 

 brane-formation whether induced by a spermatozoon or by butyric 

 acid. Thus Loeb and Wasteneys obtained the following results with 

 the unfertilized and otherwise untreated eggs of Strongylocentrotus 

 purpuratus: 



Oxygen-consumption in 



ninety minutes, 

 Solution. mgm. 



Normal sea-water 0.30 



Hypertonic sea-water ( = 50 c.c. sea-water + 9 c.c. 2| m. NaCl 



+ KC1 + CaCl 2 ) 0.67 



Normal sea-water half an hour later 0.51 



Normal sea- water twenty-one hours later 0.48 



