Equilibrium in Human Serum 



239 



though the results were not conclusive, owing to considerable 

 error in the method. When potassium (in amounts similar 

 to those normally present in serum) was added to the outside 

 fluid described in the last experiment and the system was al- 

 lowed to come to equilibrium, then it was found that — 



Concentration K in serum > concentration K in fluid. 

 Concentration CI in serum < concentration CI in fluid. 

 Concentration Na in serum — concentration Na in fluid. 



Iii other words, when working with pure serum proteins and 

 electrolyte solutions, we are able to reproduce in vitro the con- 

 ditions existing in the body and the relationships determined 

 are in the nature of the Donnan equilibrium. Furthermore, 

 as might be predicted from the Donnan equilibrium, the quan- 

 titative differences of ion concentrations in the serum and salt 

 solutions are proportionate to the protein concentration of the 

 serum. 



1 16 (2076) 



Electrometric acid-base titrations by means of the quinhydrone 

 electrode and its application under physiological conditions. 1 



By VICTOR K. LAMER 2 and T. R. PARSONS. 3 



[From the Physiological Laboratory, Cambridge University, 

 Cambridge, England.] 



It has recently been shown that an acid solution containing 

 equimolecular proportions of benzoquinone and hydroquinone, 

 a condition which is most easily obtained by dissolving the 

 crystalline addition product, benzoquinhydrone, in the medium 

 under examination, promptly produces a stable and reproducible 

 oxidation-reduction potential on a properly prepared inert elec- 

 trode, preferably of gold. In acid solutions the observed po- 



1 Read before the Physiological Society, London, January 20, 1923. 



2 William Bayard Cutting, traveling fellow, Columbia University. 



3 Working under a grant from the Medical Research Council of Great 

 Britain. 



