846 GENERAL METABOLISM [pt. iii 



least 2 hours without showing any change in internal />H, maintaining 

 independence thus against a change of 2-4 pH units in their en- 

 vironment. 



Subsequent micro-injection work has uniformly confirmed our 

 findings as regards intracellular pH. Rapkine & Wurmser injected 

 dissolved indicators into the nucleus and the cytoplasm separately 

 of the egg-cells of Strongylocentrotus lividus and Asterias rubens, and 

 could not distinguish any difference between the pH. Both nucleus 

 and cytoplasm were in the close proximity of pH 7-0. Chambers & 

 Pollack, however, did obtain a certain difference between the 

 nucleus and cytoplasm in the case of Arbacia eggs, getting values 

 of 7-6-7-8 for the nucleus, 6'6-6-8 for the cytoplasm, and 5-4-5'6 

 for the pH of cytolysis. They found, just as we had, that cytolysed 

 material in time assumes the /?H of the surrounding sea water; 

 an observation which probably explains the tendency towards 

 alkalinity which Vies had associated with cytolysis. Injury to the 

 nucleus did not affect its j&H, but the spherical nuclear remnant 

 persisting after injury gradually assumed the />H of the environment. 

 Curiously, an indicator for which the egg was normally impermeable 

 could penetrate into it through a tear in the surface if the en- 

 vironment was more acid than normal. Perhaps the plasmalemma 

 coat of the protoplasm does not form so completely in an acid 

 medium. 



Our observations on the j&H of the blastocoele cavity were greatly 

 extended by Rapkine & Prenant, who in 1925 followed the course 

 of events in detail. To begin with, in the blastula of Strongylocentrotus 

 lividus, thepH. (ascertained by micro-injection of dissolved indicators) 

 was between 7-0 and 7-3, but a little after gastrulation, as soon as 

 the primitive mesenchyme cells appeared, it rose through 8-o, at 

 which point the spicules were first formed, to 8-5, after which it 

 gradually descended again to its original value of rather less than 

 the surrounding sea water. It was evident that the rise and fall of 

 the curve (shown in Fig. 208) was associated with the process of 

 deposition of calcium for the spicules. pH 8 had already been noted 

 by Prenant to be the most favourable hydrogen ion concentration 

 in vitro for the deposition of calcite, and it is known that the spicules 

 of echinoderms are of this mineralogical form. This work was re- 

 peated on the eggs of Echinocardium cordatum, with the result that a 

 precisely similar curve was found. Rapkine & Prenant pictured a 



