SECT. 6] OF THE EMBRYO 867 



Pollack & Cohen working with the sand-dollar egg {Echinarachnius 

 parma) found a lower overall rH (about i2-o). We did no anaerobic 

 experiments but the American workers got a value of 7-9 in hydrogen. 

 No rhythmic changes occurred during segmentation nor was there 

 any localisation of reducing power in the egg-cells. These obser- 

 vations were confirmed by Chambers, Pollack & Cohen. Cytolysis 

 in amoebae produces an increased reducing power, but we were 

 never able to see this in the case of the eggs, though we expected to 

 do so in view of the statement made by Faure-Fremiet that on 

 cytolysis the reducing power for methylene blue of a given amount of 

 Sabellaria eggs rises some 30 to 40 times. Chambers, Pollack & Cohen 

 found the exact opposite to be true in the case of the sand-dollar 

 egg; i.e. it becomes less reducing as it cytolyses. We attached much 

 importance to the fact that no change in intracellular rH occurred 

 on fertilisation, for it implied that the intensity of oxidation-reduction 

 was not affected by that event, and the tremendous increase in 

 oxygen-consumption associated with it must therefore be a quantita- 

 tive rather than a qualitative change^. The same substances are com- 

 busted, we concluded, before as after fertihsation, only in less 

 quantity. This agrees with Runnstrom's view that fertilisation affects 

 the degree of dispersion of the egg-colloids, and increases the acces- 

 sibility of the enzyme surfaces for their appropriate substrates. We 

 also found the rH to be quite constant as far as the 8-cell stage. 



Cannan investigated the oxidation-reduction potential of echino- 

 chrome, the reversible natural rH indicator extracted from the 

 eggs of Arbacia. This pigment takes a definite place on the rH scale, 

 but does not form a dissociable compound with oxygen, so that its 

 role in the cell must be an activator rather than a carrier of oxygen. 

 The pigment may therefore be an effective oxygen activator in the 

 cell, much as the " Atmungsferment " of Warburg is supposed to be. 

 In this case, the concentration of its reduced form present would be 

 of great importance, and this would be determined by the oxidation- 

 reduction potential of the cell or the phase in which the pigment 

 is present. Arguing in this way, Cannan pointed out that only a 

 very small change in intracellular rH might increase or decrease the 

 metabolic rate or oxygen consumption by a hundredfold, so that our 

 inability to find any change in rH of the cell at fertilisation — a time 



^ See further, on this subject, p. 626. Fertihsation involves " the opening of doors 

 within the egg-cell". 



