3o6 PROTOPLASMIC ACTION AND NERVOUS ACTION 



The demarcation potentials of living tissues appear 

 to exemplify this general condition.^ In the usual 

 method of studying these potentials in muscle or nerve 

 the normal cell surface in part of the tissue is first altered 

 by mechanical or other means. The electrodes leading 

 to the galvanometer then touch two surfaces, altered 

 and normal, which differ in their physico-chemical 

 condition; a corresponding potential difference is shown, 

 the injured region being negative. Hence the term 

 "alteration current" for the current between the two 

 regions. Loeb and Beutner found the same to be true 

 for a simple organic membrane like an apple skin; 

 when one region is crushed, this region shows itself 

 negative to an unaltered region; potential differences 

 of 20 to 100 milH volts were observed in different ex- 

 periments, the values varying with the concentration 

 of the salt solution in contact with the tissue.^ 



Loeb and Beutner found also that the potential 

 changed with changes in the concentration of the 

 surrounding solution in a manner similar to that observed 

 by Macdonald for nerve. To produce a constant 

 arithmetic change in the potential-difl'erence, the con- 

 centration of the salt had to be changed in a constant 

 ratio; i.e., to a geometric series of concentrations 



^ The importance of the Donnan membrane potential (potential 

 across a membrane permeable to only a part of the ions present), in 

 the case of protein solutions separated from electrolyte solutions by 

 collodion or similar membranes, has recently been demonstrated by 

 Loeb in an important series of researches (summarized in his book, 

 Proteins and the Theory of Colloidal Behavior). In this case a colloidal 

 ion (protein) is the one to which the membrane is impermeable. In 

 livdng tissues, however, with protein ions in about equal concentration 

 on both sides of the membrane (in protoplasm and in lymph) this source 

 of potential can scarcely play a part. 



2 Biochem. Zeitschrift, XLI (1912), i; cf. p. 22. 



