CYTOPLASM 



157 



electrode E = o) and the value of p^ in the system are used as rectangular 

 coordinates, the curves of constant hydrogen pressure (rjj) are sloping 

 lines. If two of the three quantities: electric redox potential E, the exponent 

 of hydrogen pressure r^ and the exponent of hydrogen ion concentration 

 pjj, are known, the magnitude of the third one can be read from the diagram 

 in Fig. 103. Since the redox system is only determined by its electric poten- 

 tial E, it follows that in biological systems both the t^ value and its corre- 

 sponding Pjj value should be given. On this condition the rj^ value may be 

 identified with the redox potential, as is usually done in biology. 



TABLE XVIII 



Pjj and rjj SYMBOLISM 



Actual acidity 

 Ph 



Redox system 



■■H 



Starting point. . . 

 Dissociation . . . 

 Law of mass action 



Exponent 



Inter\^al 



hydrogen ion cone. cH+ 

 H2O ^ H+ + OH- 

 cH+-cOH- = 1 0-1* 



Ph = -log cH+ 

 Pjj varies from 0-14 



hydrogen pressure tHg 

 2H2O ^ 2H2 + O2 



(tH2)2-t02 = IO-«2 



r„ = -log tHo 



■■H 



rjj varies from 0-41 



TABLE XIX 



REDOX POTENTIAL (rjj) OF CERTAIN PROTOPLASTS 

 (according TO NEEDHAM, 1 92 5) 



Sea-urchin egg 



Amoeha proteus 



Salivary gland of Chironomus . 



Ph 



6.5 

 7.6 



7-2 



^H 



19-21 

 17-19 

 19-20 



Just as the heteropolar valency bonds are strongest at a certain pjj, 

 namely at the I.E. P., there is an optimum value of Tjj at which the 

 homopolar valency bonds are the least endangered. It has already been 

 pointed out that cystine bridges are broken down at high hydrogen 

 pressures, i.e., at low rjj-values. At high values of rjj they are re- 

 established. A high rjj is, however, also capable of loosening bonds 

 (oxidation). As shown by Staudinger (1957a, p. 13), the glucoside 



