SECT. 6] OF THE EMBRYO 863 



he supposed that the entry of calcium carbonate from the shell would 

 lead to the increasing concentration of carbonate in the tissues which 

 he found experimentally. He suggested that it might be possible to 

 find by calculation that amount of carbonate in the functioning 

 tissues. It was known that the concentration of protein in the em- 

 bryonic body rises during incubation, so Murray suggested that, as 

 proteins would act as anions at the pH found, they would replace the 

 diminishing chloride. Unfortunately, we may be quite sure that 

 the pH. as found by the crushing method employed by Murray is not 

 that of the uninjured cells, so that this calculation loses most of its 

 force. Murray's observation, however, that the point of greatest 

 increment on the rising protein curve came some 4 or 5 days after 

 the point of greatest decrement on the falling chloride curve, remains 

 quite true. "The results of our observations", said Murray, "which 

 show that the electrolytes probably change several days before the 

 protein, and the latter several days before the fat, lead to the con- 

 clusion that the processes of chemical differentiation are not to be 

 described by a concept of dynamic equilibrium but rather by a notion 

 of 'follow my leader'. The leader in this case is presumably the most 

 rapidly permeating, reactive, and mobile molecule and tentatively we 

 ascribe this role to the CO2 of metabolism." What does this mean? 



Parallel experiments to these were made by Woglom on the embryo 

 of the rat, using a technique which included the fine mincing of the 

 tissue, and the electrometric determination of the pH on the resulting 

 cell-emulsion. He got values of /?H 7-04 to 7-36, with an average at 

 pH 7-14. Then Ruzicka, who did not give any details of the method 

 he employed, but presumably worked with minced or crushed cells, 

 obtained the following series : 



Table 99. 



Frog (Ranafusca) pH 



Unfertilised eggs ... ... ... ... 6-6 



Morulae ... ... ... ... ... 6-i-6*2 



Gastrulae ... ... ... ... ... 6-4 



First appearance of medullary plate... ... 6'2 



First appearance of tail bud ... ... ... 6*o— 6'2 



Larva 6 mm. long ... ... ... ... 6-4 



Appearance of external gills ... ... ... 6-7 



Disappearance of external gills ... ... y-o-y-l 



Larva 15 mm. long ... ... ... ... 6-8 



Larva 22-7 mm. long ... ... ... ... 6-9 



First appearance of hind legs ... ... 7-8 



Completely formed hind legs... ... ... 7-0 



Immediately after metamorphosis ... ... 7-2 



Sexually mature frogs ... ... ... 7'5-7'9 



