SECT. 6] 



OF THE EMBRYO 



865 



agreement here with the fragmentary resuhs of Gueylard & Portier, 

 who found blood hydrogen ion concentrations ranging from 8-4 to 

 8-1 on the last 2 or 3 days of the chick's development. The few 

 figures collected by Hajek would seem to indicate that the rise to the 

 adult pH level in human blood from the acid side has attained 

 completeness at birth. 



Millet has worked on the blood and tissues of the embryonic 

 rabbit, using the glass electrode, and Mendeleef has done similar 

 experiments on the blood of the guinea-pig, using colorimetric 



Maternal Embryonic 



M;ilet(rabbit) 



pH 



22 23 24 25 26 27 28 29 : 

 Days 



Mendeleef guinea-pig 

 O Embryonic serum 



Maternal level 



E mbryonic tissues 



40 45 50 55 

 Days concepbion age 



Fig. 21 



Fig. 219. 



methods. From Figs. 218 and 219 it can be seen that in each case 

 there is a passage from the acid side to slightly above neutrality, 

 and this agrees with the work of Ruzicka; Buytendijk & Woerdemann; 

 and Cohn & Mirsky. But there is Httle to show that these curves 

 may not be due to a steady increase in the amount of blood taken 

 for sample, rather than to a real increase in pH, and as yet too 

 much emphasis must not be laid upon any of these conclusions. 



6-3. rH in Embryonic Life 



Closely related to the />H is another factor, less generally used by 

 biologists, the rH. Oxidation-reduction processes, like acid-base 

 equilibria, have an intensity as well as a capacity factor. Just as 

 we may speak of the hydrogen ion concentration, distinguishing 

 it from the total amount of acid or alkali present, ascertainable by a 

 titration which mobilises the factor titrated as fast as it is used up 

 until no more is left — so we may speak of the oxidation-reduction 

 potential, meaning the intensity of electron transfer in the system, 



