FERTILISATION 187 



amount of oxygen taken up by the egg of the sea-urchin Arbacia 

 on fertilisation was quantitatively measured. The oxygen disappear- 

 ing from the sea-water in which the eggs had stood for some time 

 was determined by the Winkler method, by titration with sodium 

 thiosulphate. Warburg found that for a quantity of eggs that 

 contained 28 milligrams of nitrogen, which roughly corresponds to 

 about 4 million eggs, 4-5 cubic centimetres of oxygen were taken 

 up in the course of the first hour following fertilisation. The same 

 quantity of unfertilised eggs consumed O'S-0'7 c.c. oxygen in this 

 time, that is, the fertilised eggs used up six to seven times more 

 oxygen than the unfertilised. As early cleavage and development 

 progressed, more and more oxygen was consumed, but in the absence 

 of oxygen all development was stopped. In the 32-cell stage 6'8 c.c. 

 ox*yge'n were taken up, as compared with the 4 c.c. consumed in the 

 first hour after fertilisation. If the eggs were placed in hypertonic 

 sea-water the normal rate of oxidation could be increased as much 

 as ten times. In normal sea-water the fertilised eggs require a 

 constant amount of oxygen to reach a definite stage, but this stage 

 could be reached with half this oxygen consumption if the eggs had 

 been entered by more than one sperm. Since there is this great 

 increase in the respiratory exchange of the egg on fertilisation, and 

 as this always shows a certain amount of progressive increase as 

 development advances, it is natural to conclude that the energy 

 liberated in the ovum by this increased oxygen consumption is 

 correlated with the mitotic activity, and the various processes of 

 morphogenesis taking place in the fertilised egg. It is clear, 

 however, that this is not the case. Warburg l has shown that if 

 the fertilised egg is placed in strong hypertonic sea-water, or if a 

 little phenylurethane (^Vir N) is added to the sea-water, all cell 

 formation is inhibited, although the egg continues to live and 

 undergoes a certain amount of development in the absence of cell 

 formation. These eggs, however, consume as much oxygen as those 

 in which normal cell formation and mitosis take place. 



Moreover the oxygen consumption of the egg obviously fails to 

 keep pace with the increase in its morphological structure, for 

 in the sixth hour following fertilisation, although the egg is now 

 composed of 32 cells, the oxygen consumption has only increased 

 from 4-6'8 c.c. per hour. In another experiment of Warburg's a 

 larger number of eggs was used, 13'2 ing. of oxygen was consumed 

 in the 8-cell stage, while in the 32-cell stage only 20'5 mg. was 

 absorbed. Thus while the oxygen consumption doubled in amount, 

 the cell structure had increased four times. In these results we 



1 Warburg, " Uber die Oxydationen in lebenden Zellen," Arch. f. ges. 

 Physiol., vol. Ixvi., 1910. 



