PROTOPLASMIC STRUCTURE 93 



The importance of adsorption-potentials is shown 

 most clearly in the phenomena of electrical endosmose, 

 which are of great physiological importance and will be 

 considered briefly below. The marked influence which 

 slight quantities of acid and alkali have in altering the 

 phase-boundary potentials, especially in the neighbor- 

 hood of the isoelectric point, is a fact of special biological 

 interest. Near this point the effect of variations in the 

 H-ion concentration upon the phase-boundary potentials 

 is at its maximum; farther from the isoelectric point 

 the difference caused by a given change in the H-ion 

 concentration is relatively slight.^ 



The reactions of the tissue fluids in higher animals are 

 slightly on the alkaline side of neutrality, and the reaction 

 of the living protoplasm (because of the higher tension 

 of CO2 within the cell) is presumably somewhat less 

 alkaline and is probably not far from the isoelectric 

 point of some of the structural proteins. Hence slight 

 variations of the H-ion concentration within the cell 

 should have a correspondingly great effect upon the 

 boundary-potentials of the corresponding cell-structures. 

 Variations in the H-ion concentration of the cell-medium 

 would affect first of all the boundary-potential of the 

 cell as a whole; i.e., that existing across the plasma 

 membrane, and this is probably the chief reason why 

 living tissues are frequently so sensitive to changes in the 

 external H-ion concentration. As already pointed out, 

 this sensitivity has in some cases become the controlling 

 factor in regulatory processes of vital importance to 

 the whole organism, as in the respiratory nerve, cells of 

 vertebrates, which show an accelerated rhythm in 



^ Cf. Haber and Klemensiewicz, loc. cit. 



