OF VITAL PHENOMENA 125 



The emf of the frog's skin has been the object of many in- 

 vestigations, but the results so far are for the most part con- 

 fusing. Schwartz (191 5) found that the electrical conductivity 

 of the frog's skin is increased when the nerves to the skin glands 

 are stimulated. It is probable that the emf of the frog's skin 

 is analogous to the action current, or more nearly to the current 

 of injury of muscle, and is due to the permeability of one side 

 of the gland cell and semipermeability of the other, the latter 

 being the seat of the emf. The experiments of Bayliss (1908) 

 tend to support this view. On passing an alternating current 

 through the frog's skin, he observed that it acted to a certain 

 extent as an electric rectifier, allowing a current to pass more 

 easily in one direction than in the other. The same effect was 

 produced by a parchment paper membrane separating a solution 

 of congo red from water. This dye dissociates into Na ions 

 and enormous anions. If the cathode is placed in the water, 

 the current is carried through the membrane by the Na ions, but 

 if the anode is placed in the water, the anions attempt to pass 

 through the membrane to the anode, but are unable to do so. 



Perhaps much of the confusion arising from the study of the 

 emf of living tissues is due to the fact that they are made of 

 more than one kind of cell, and that the permeability of the cells 

 may be changed by the experimental procedure. Consider, for 

 example, the excised muscle. If it is bathed on all sides by 

 lymph or blood, any emf observed is probably due to the muscle 

 cells, but if one electrode is connected to it by a more concen- 

 trated solution and the other by a dilute solution of electrolytes, 

 the system may form a concentration cell in which the peri- 

 mysium or muscle sheath is the chief membrane concerned. The 

 fact that porcelain membranes may act in this capacity, shows 

 that relatively permeable membranes must be taken into con- 

 sideration, even membranes allowing an appreciable amount of 

 filtration. Oker-Blom (1901) studied what he called the contact 

 potential between muscle and certain solutions. This work was 

 extended by Briinings (1907) who attempted to prevent the in- 

 jurious effect of diluting the salt solutions by the addition of 

 sugar to make them isotonic. He found the contact potential 

 between frog's muscle and sugar solution to be 50 millivolts, with 

 the sugar side positive, and the same result was obtained with 



