858 



GENERAL METABOLISM 



[PT. Ill 



Titratable AcicLit3r 



present in it. The amniotic and allantoic figures present analogous 

 curves. Aggazzotti found that if infertile eggs were incubated there 

 was no change at all in the pH of their white, but that the yolk 

 pB. rose just as in the fertile egg, but not so far, i.e. up to pH 6-2 

 or thereabouts, and never further. This presents an analogy with 

 BelHni's findings on the viscosity of incubated infertile and fertile 

 eggs, where the same change seemed to go on in the yolk of the 

 infertile egg, but to a less extent, while the white was far less 

 affected. It is probable that these phenomena are due to the 

 presence of enzymes in the yolk and not in the white, a statement 

 generally true, as the Section devoted to enzymes will show. These 

 enzymes will naturally begin to work at the beginning of incubation 

 irrespective of whether the 

 egg is fertile, and will pro- 

 duce some of the changes asso- 

 ciated with development, but 

 it is reasonable to suppose that 

 the embryo exerts a furthering 

 influence upon their activity. 

 This was indeed the explana- 

 tion adopted by Aggazzotti. 



The significance of all these 

 changes is not easy to under- 

 stand. It must, for instance, 

 be important that at the end 

 of development the embryo is surrounded on all sides by liquids of acid 

 reaction. The fact that the slope of the two curves (the descending one 

 of the white and the ascending one of the yolk) is very much alike, led 

 Aggazzotti to suggest that there was some simple relation between 

 them, such as a transfer of hydrogen ions from the yolk to the white. 

 But it is certain that events are more complicated than that. One 

 very interesting fact appears, if the behaviour of the amniotic fluid in 

 Fig. 211 is compared with that in Fig. 212, for it is then seen that, 

 though the final pH of the amniotic fluid is much the same as that 

 of the yolk at the beginning of development, their total acidities are 

 by no means the same, the former being only half the latter. It is 

 obvious, therefore, that the dissociation constants of the acids re- 

 sponsible are very different, being much greater in the case of the 

 final amnios pH than in that of the initial yolk. 



Fig. 21Q. 



