MEMBRANE POTENTIALS 



131 



Substituting \/y(y + z) for x in the term - we get 



Vy(y 



%&! 



Hence at 18C. the P.D. should be = y log (l + -) millivolts. 



We will now show that from the term \n + - the influence of 



y 



pH on the P.D. as expressed in the curves of Fig. 41 can be derived. 



When we add little HC1 to isoelectric gelatin, we increase the 



amount of gelatin chloride formed and hence the value of z. 



Hence, the P.D. should increase since it depends on log (l + -j. 

 We also increase the value of y, but z and y will not increase at 



the same rate, z can be calculated from the equation - = - 



y x 



z = x 2 - y 2 = (x + y)(x - y) 



y y 



When little acid is added to isoelectric gelatin the value of z 

 rises more rapidly than the value of y, while when more acid is 

 added the reverse happens. This is obvious from Table XIV 

 comparing the variations of z and y upon the addition of increas- 

 ing quantities of HC1 to isoelectric gelatin. 



TABLE XIV 



