SECT. 6] OF THE EMBRYO 849 



inserting them between rather than through the cells of the wall of 

 the blastula, the pH of 8-4 was found for the interior fluid, and 

 that injury to the cells surrounding it accounted for the lower 

 hydrogen ion concentrations found by Rapkine & Prenant^. 

 Chambers & Pollack concluded, therefore, that the pH of the liquid 

 filling the cavity is until metamorphosis exactly the same as that of 

 the sea water in which the embryos are placed. The regularity of the 

 curve obtained by Rapkine & Prenant is, of course, an argument 

 against these criticisms, but, in view of the difference of opinion, 

 similar experiments should certainly be undertaken again. 



Electrometric measurements of j&H were begun by Vies, Reiss & 

 Vellinger in 1924, who made a thick suspension of eggs, freezing them 

 solid very rapidly, pounding up the hard mass, and then placing the 

 electrodes in contact with it as it melted. Unfortunately this procedure 

 did not give one definite potentiometer reading, but a whole ascending 

 curve, so that it was necessary to choose a time for taking the reading. 

 Vies, Reiss & Vellinger chose the moment when the thermometer 

 indicated 0°, and calculating from that they obtained for normal 

 Strongplocentrotus eggs an average value of j&H 5-3, or for 18° 5-1. 

 For eggs from which the jellies had been first of all removed by 

 potassium cyanide the value was 6-3 for 18°. The three investigators 

 explained this more alkaline figure as being due to the easier escape 

 of carbon dioxide in the case of the dejellified eggs, though, as the 

 whole system was one more or less homogeneous paste, it is difficult 

 to understand this argument. In general, they concluded that the 

 electrometric method gave results which fully confirmed their work 

 with the microcompression colorimetric method. This was doubt- 

 less true, but it seemed to other workers that the reason was 

 mainly because the principal source of error, i.e. cytolysis and acid 

 production, was the same. Injury is almost certainly done to cells 

 on freezing by the formation of ice crystals, and even if the acid pro- 

 duction of cytolysis is in abeyance at the low temperature, it will come 

 into play as the temperature rises, even in all probability before 0° 

 is reached. 



Vellinger, however, has continued researches in this direction, and 

 the method has been used by the Strasburg school in the case of 

 many types of cells other than eggs and embryos. Vellinger used a 



1 But would the cytolysis of two or three cells suffice to acidify the whole blastocoele 

 cavity? 



