CHAPTER 5 



THE METABOLISM OF EGGS, I 



Oxygen uptake. In 1908 Warburg did some famous experiments 

 showing that fertiHzation caused a sharp and immediate increase 

 in the respiration of sea-urchin eggs. The resuhs of a more 

 recent, manometric experiment on this subject, with KOH in the 

 centre well of the flask, are given in Fig. 9. The difference be- 

 tween the pre- and post-fertilization rates of O2 uptake is about 

 600%. During the first five minutes after the addition of sperm- 

 atozoa to the egg suspension, respiration appears to have com- 

 pletely stopped; but this is an illusion caused by the transient pro- 

 duction of egg acid which takes place at fertilization (q.v.). This 

 acid displaces CO2 from the bicarbonate in the sea water at such a 

 rate that the KOH in the centre well cannot absorb it immediately. 

 As a result, the negative pressure in the manometer, due to the 

 disappearance of oxygen, is temporarily masked by the positive 

 pressure of the evolved COg. 



In spite of the experiments of Loeb & Wasteneys (1913) on 

 starfish eggs, in which no comparable rise in respiration after 

 fertilization was found, the belief used to be widely held that 

 fertilizafion was associated with an increase in oxidative activity, 

 and that since an embryo would have to do more work, it would 

 obviously require more oxygen than an inert, unfertilized egg. As 

 we shall see, this led to further attractive but untenable ideas, for 

 example that 'cytochrome' is thrown into circulation at fertiliza- 

 tion. A new light was shed on the famous phenomenon of in- 

 creased O2 uptake at fertilization when Whitaker (1931^,6) 

 pointed out that though O2 uptake increased when the eggs of 

 Arbacia punctidata, Fucus vesiculosus and Nereis succmea were 

 fertilized, there was a negligible increase in the case of Sabellaria 

 alveolata (Linn.), and a decrease in the eggs of Cumingia tellinoides 

 and Chaetopterus variopedatus (Fig. 10). Nor is there any increase 

 in O2 uptake when the eggs of Saxostraea commercialis (Iredale & 

 Roughley) are fertilized (Cleland, 1950^), in the frog's egg 

 (Brachet, i934Z»), nor in some batches of eggs of Urechis caupo 

 (Tyler & Humason, 1937). The next discovery of interest in this 



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