FERTILISATION 235 



each nuclear division one-half of the mass of each original chromo- 

 some goes into the nucleus of each of the two resulting cells. But 

 during the resting period which elapses until these nuclei are ready 

 to divide again, each chromosome grows to its original size, and then 

 a new division occurs. It is quite possible that the oxygen which is 

 required for the process of cell division is needed for the synthesis 

 of nuclein or chromatin substance. The fact that the rate of 

 development is influenced by temperature, in much the same way 

 as are chemical reactions, supports the idea given above that the 

 essential feature of fertilisation consists in the starting or the 

 acceleration of a chemical reaction which is going on steadily in the 

 egg. Loeb was disposed to conclude, therefore, that the spermatozoon 

 acts as a positive catalyser, but further evidence has led him to reject 

 this idea as improbable. He pointed out that, if it were correct, 

 normal sea-urchin eggs should segment if kept for a sufficiently long 

 period, and that it ought to be possible to induce segmentation by 

 applying heat, since heat is known to accelerate chemical reactions, 

 but neither of these results could be obtained. 



He then suggested the possibility that the spermatozoon, in 

 conjugating with the ovum, removed from the latter a negative 

 catalyser or condition whose existence in the ovum somehow inhibits 

 the process of development. This suggestion seemed to provide an 

 explanation of the secretory phenomena, which, on Loeb's hypothesis, 

 are the cause of the membrane formation. "Finally, we may be 

 able to understand a fact which [has been] observed in the eggs of 

 a starfish, and which has not yet been mentioned, when the eggs 

 of Asierina or Asterias are allowed to ripen, they will die within a 

 few hours unless they develop either spontaneously or through the 

 influence of sperms or some of the above-mentioned agencies. The 

 disintegration which leads to the death of the non-developing egg is 

 obviously due to an oxidation, since I found that the same eggs 

 when kept in the absence of oxygen will not disintegrate. We 

 know that oxygen is an absolute prerequisite for the development 

 of the fertilised egg" [but this statement is disputed by Delage]. 

 The fact that oxygen is a poison for the mature but non-developing 

 egg shows that the chemical processes which occur in the unfertilised, 

 non-developing egg must be altogether different from those which go 

 on in the developing egg of the starfish. 1 



1 Loeb, loc. cit. See also "The Toxicity of Atmospheric Oxygen for the 

 Eggs of the Sea-Urchin after the Process of Membrane Formation " ; " On 

 the Necessity of the Presence of Free Oxygen in the Hypertonic Sea-water 

 for the Production of Artificial Parthenogenesis " ; " On the Counteraction of 

 the Toxic Effect of Hypertonic Solutions upon the Fertilised and Unfertilised 

 Egg of the Sea-Urchin by lack of Oxygen," Univ. of California Publications : 

 Physiology, vol. iii., 1906. See also " Versuche iiber den Chemischen Charakter 

 des Befruchtungsvorgangs," Biochem. Zeitsch., vol. i., 1906. " Weitere Beobacht- 



