868 GENERAL METABOLISM [pt. iii 



when the respiratory rate abruptly and greatly increases — involved 

 no contradiction. In the hypothetical system pictured by Cannan, 

 very wide metabolic latitude is combined with stability of rH, i.e. a 

 poised oxidation-reduction potential, and this is what actually seems 

 to be the state of affairs in the living cell. 



Cannan pointed out that in the eggs of Arbacia echinochrome is 

 in the fully oxidised state, but that in those of Echinus it is 

 partially reduced. As the mid-point of its rH titration curve at 

 pW 7 is about rH 6, it may be concluded that the cell-granules 

 of the eggs of Arbacia are more oxidising than this, while those of 

 Echinus esculentus eggs are at about that figure. From the work of 

 Vies & VelHnger, then, we may conclude that these portions of the 

 egg-cell have a rather acid />H, and from that of Cannan that they 

 have a distinctly more reducing rH than the rest of the cell. Such a 

 state of affairs may be usual in cells; thus mitochondria reduce Janus 

 green, a very reducing dye (Needham & Needham), and Cannan 

 found that hermidine, a natural indicator contained in plant cells, 

 was held reduced there although active photosynthesis with oxygen 

 production was going on, and although the micro-injection method 

 in the hands of Rapkine & Wurmser, and other indicator work by 

 Brooks, had demonstrated the overall rH of plant cells to be about 17. 

 The living cell is without doubt extremely heterogeneous. 



Micro-injection studies of intracellular rH were extended by 

 Rapkine & Wurmser, who determined the average rH of nucleus 

 and cytoplasm separately in the eggs of Strongylocentrotus lividus and 

 Asterias rubens. There was absolutely no difference, both lying be- 

 tween rH 19 and 20-5. Thus the old idea of the nucleus as an 

 "oxidation-place" (LiUie and Unna) is devoid of foundation. It 

 remains possible, of course, that oxidations may go on to a greater 

 extent in the nucleus than in the cytoplasm, though there is no evi- 

 dence for this view; what is certain is that there is no greater intensity 

 of oxidation-reduction in the nucleus than in the cytoplasm. They did 

 not follow the eggs through later stages because of the disappearance 

 of the germinal vesicle. Rapkine also studied the rH of the liquid 

 fining the blastocoele cavity in echinoderms, micro-injecting indi- 

 cators into it. He found it to be about 19. As he had strong reasons 

 for supposing that free oxygen was circulating in it, it was clear that 

 molecular oxygen was quite inactive as regards the oxidation- 

 reduction equiHbria. As the rH of this system was inferior to that 



