840 GENERAL METABOLISM [pt. m 



proceeded the deeper the eggs stained, and the more difficult it 

 was to wash the stain out. He concluded that the internal pH 

 was on the acid side of neutrality, but not much below 6-o. More- 

 over Warburg; Harvey; and Herlant all found by staining with 

 neutral red that the contents of the echinoderm egg was more acid 

 than sea water. Still earlier work by Keeble & Gamble, who had 

 succeeded in staining Hippolyte and Mysis eggs with litmus, had 

 indicated an internal pYL of between 4 and 3, but it is probable that 

 the eggs so stained were dead. 



Other work involving the staining method was even less illuminating. 

 Faure-Fremiet, exposing the eggs of the polychaete worm, Sabellaria 

 alveolata, to the action of such dyes as Nile blue hydrochloride, Nile 

 blue sulphate and brilliant cresyl blue, concluded that a pYi of 

 nearly 13 was reached at fertilisation. This extraordinary result was 

 clearly due to the use of dyes which even under the best conditions 

 are not good pH indicators, and which could not be trusted in a 

 medium containing fatty substances, for which they have a special 

 affinity. Lewis, again, growing embryonic fibroblasts on nutrient 

 media to which indicators had been added, could not get any of 

 them to stain until death occurred, whereupon they indicated a 

 cytolysis />H of below 5-0. 



The study of intracellular /?H by vital staining received a consider- 

 able impetus in 1925 from the work of Rous and his collaborators, 

 who employed the method largely on the whole organism in mam- 

 mals. Using his method, Harde & Henri found the following values 

 for the mouse: 



Uterine wall ... ... 6-0-6-2 



Placenta ... ... ... 7-2-7-4 



Embryonic skin ... ... 5"6-5*8 



Maternal skin ... ... 7-4-8-6 



Embryonic blood ... ... 5-8 



This last value was in good agreement with another obtained in a 

 similar way by Mendeleef on guinea-pig's blood, which she found to 

 be at pa 5*8, although the maternal blood was />H 7-4. The tissue 

 fluid of the embryo (how prepared?) she found to be at/?H 6-o. 



It is, of course, doubtful as to what exactly is meant by intra- 

 cellular />H or the internal j&H of the egg. There m.ust without doubt 

 be numerous phases, perhaps of ^videly differing />H, and all that we 

 measure directly by the various methods is the "j^H globale" or 

 overall pYi of the cell. Lucke drew attention to the fact that, even 



