SECTION V 

 ELECTRICAL CHANGES IN LIVING TISSUES 



THE material composing living cells and tissues is permeated throughout 

 with water containing electrolytes in solution. All salts, as we have seen, 

 undergo ionic dissociation in watery solution a dissociation which, in the 

 concentrations occurring in the animal body, must be nearly complete. 

 When an electric current passes through the living tissues it is carried by the 

 charged ions formed by the dissociation of the salts. Thus, n/10 solution 



+ 

 of sodium chloride contains almost entirely Na and Cl ions. In addition to 



these charged inorganic ions, the cell protoplasm contains in solution or 

 suspension various colloidal particles which in many cases are themselves 

 charged. By the presence of these colloidal particles marked differences 

 may be caused in the distribution of the inorganic ions owing to the power 

 of adsorption possessed by the colloids for many inorganic salts. It is 

 evident that any unequal distribution of the charged ions or colloidal particles 

 in a tissue or on the two sides of a membrane may give rise to corresponding 

 unequal distribution of electric charges, and therefore differences of potential 

 between different parts of the tissue, which under suitable conditions may 

 find their expression in an electric current. It is therefore not surprising that 

 practically every functional change in a tissue has been shown to be associated 

 with the production of differences of electrical potential. Thus all parts of 

 an uninjured muscle are isopotential, and any two points may be led off to a 

 galvanometer without any current being observed. If, however, one part 

 of the muscle be strongly excited, as, for instance, by injury, so that it is 

 brought into a state of lasting excitation, it will be found that, on leading 

 off from this point and a point on the uninjured surface to a galvanometer, 

 a current flows through the latter from the uninjured to the injured surface. 

 Every beat of the heart, every twitch of a muscle, every state of secretion of 

 a gland, is associated in the same way with electrical changes. In most 

 cases the electrical changes associated with activity have the same general 

 character, the excited part being found to be negative in reference to any 

 other part of the tissue which is at rest. The uniform character of the 

 electric response in different kinds of tissues suggests that an accurate know- 

 ledge of the changes in the distribution of charged ions responsible for the 

 response ought to throw important light on the intimate nature of excitation 

 generally. It may be therefore advisable to consider more closely the 



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