74 FERTILIZATION 



mgN. The effect is a transient one, the rate of 'glycogenolysis' 

 nearly returning to the pre-fertiHzation level ten minutes after 

 fertilization. In spite of the acid production at fertilization, this 

 breakdown is not associated with the accumulation of lactic acid 

 or any of the tricarboxylic acids; moreover, the amounts of in- 

 organic phosphate, pyrophosphate and hexose phosphates have 

 been said not to change at fertilization (Runnstrom, 1933; Zie- 

 linski, 1939; Orstrom & Lindberg, 1940), though we shall see in 

 the next chapter that recent experiments, in which more refined 

 methods were used, do not entirely support these findings. If 

 the low R.Q. during the first few minutes after fertilization is 

 linked to carbohydrate metabolism, which seems unlikely, we must 

 conclude that an obscure and transient reaction, involving the in- 

 complete oxidation of carbohydrate and about which, at present, 

 there are practically no clues, must occur, transiently, at fertiliza- 

 tion. Both Brachet, in Chemical Embryology (1950), and Runn- 

 strom, in The Mechanism of Fertilization in Metazoa (1949), seem 

 to favour the view that the disappearance of polysaccharide at 

 fertilization has something to do with the hexose monophosphate 

 pathway. If this system is only acting as a partial by-pass of normal 

 glycolysis, lactic or pyruvic acid should be formed and oxidized in 

 the usual way. If, on the other hand, the hexose monophosphate 

 reaction is concerned with nucleotide metabolism, why should it 

 only last for ten minutes after fertilization ? The lack of answers to 

 these questions indicates, as usual, the need for more experiments. 

 Lipid metabolism. The low R.Q. at fertilization suggests the 

 transient oxidation of fats at this time, quite apart from the possi- 

 bility of fats being an important endogenous substrate before fer- 

 tilization. The most systematic study of this subject is due to 

 Ohman (1945), who found that the total lipid content of the eggs 

 of Echinocardiiim cor datum, which is about 200 mg/ioo mg N, 

 decreases for some seven hours after fertilization. Of these lipids, 

 the choline-containing phosphatides or lecithins decrease as de- 

 velopment proceeds, while the cephalins or non-choline-containing 

 phosphatides increase. Ten minutes after fertilization, 29% of the 

 free cephalin in the egg becomes bound to proteins. The difference 

 between free and bound cephalin is based on the solubility 

 of the former in ether-chloroform mixtures and the solubility of 

 the latter in chloroform-ethanol mixtures. In an earlier paper, 

 Ohman (1942) reported that, at fertilization, there was a reduction 



