174 



Scientific Proceedings (60). 



of its vital properties. This shows that the alteration theory can 

 by no means claim a general applicability. 



5. The alteration theory certainly does not give any point of 

 view concerning the physical nature of the currents produced by 

 tissues. Among the more recent attempts to solve this problem 

 the so-called membrane theory is especially prominent. This 

 theory was put forward by Ostwald in 1895 on the assumption 

 that a semipermeable membrane is more permeable for cations 

 than for anions. It is however not thoroughly justified from a 

 physical standpoint either and Tammann and Walden who tried to 

 prove it by means of analytical methods in Ostwald's laboratory 

 have got contradictory results. Apparently therefore an experi- 

 mental study of the E.M.F.'s produced by tissues and their arti- 

 ficial imitation, is a more promising method for the solution of 

 the problem in question. 



6. One of the most characteristic properties of the E.M.F. 

 produced by tissues is the positivizing effect of water and of dilute 

 salt-solutions as shown by the experiments of Biedermann and of 

 Mac Donald described above. Dr. Loeb and the author have 

 studied this phenomenon in a more quantitative way, namely with 

 uninjured plants. 



An artificial imitation of this property has been possible. A 

 systematic study of cell arrangments composed of aqueous and 

 water immiscible electrolytes (undertaken by the author) has 

 shown that all water immiscible acid substances — used as ventral 

 conductor show the same phenomena as living tissue, especially 

 solutions of fatty acids in substituted phenols (as found recently 

 by Dr. Loeb and the author). 



The presence of a water immiscible acid (most likely a fatty 

 acid) in the skin or membrane surrounding the tissue is therefore 

 essential for this positivizing effect, not a selective permeability 

 to cations as one would expect from Ostwald's theory. (Also the 

 negativizing effect of K salts which was observed by Biedermann 

 on muscles could be imitated by means of pure water immiscible 

 substances.) 



7. These experiments make it possible to investigate the 

 physical nature of the single potential differences which compose the 

 E.M.F.'s produced by tissues. For the cell arrangements of aque- 



