OF ARTS AND SCIENCES : JANUARY 9, 1872. 345 



left, apparently, no doubt of the existence of electrical currents in 

 nerve and muscle. 



Physiologists have been led from considering the anomalous con- 

 tractions of the galvanoscopic frog to conclude that there exist in the 

 muscles and nerves of man, of fishes, and in the various organs 

 of the lower forms of life, currents which have determinate directions. 

 The earlier investigators tested for the presence of these currents by 

 touching the organs or parts to be examined with the bare terminals of 

 the galvanometer ; indeed, this method of investigation is still pursued 

 by certain physiologists. 



The evidence of the existence of animal currents produced by touch- 

 ing the muscles with the bare terminals of a galvanometer or an elec- 

 trometer is entirely insufficient to prove that electrical currents circu- 

 late in the muscular or nerve tissues. One is baffled at every step by 

 the dissimilar composition of the terminals ; by the changes which they 

 undergo from the action of the air upon the fluids adhering to the sur- 

 face of the platinum ; and by the influence of heat. 



It is true that by experimenting with the bare terminals one can 

 state a difference in the chemical nature of the different tissues of the 

 muscle or nerve ; we cannot, however, conclude that electrical currents 

 exist in a determinate direction between such tissues ; indeed, in many 

 cases the galvanic action is evoked by the action of the metallic plates 

 of the terminals. This unequal composition of the two electrodes can 

 be overcome, as Matteuci has shown, by using amalgamated zinc ter- 

 minals placed in a saturated solution of sulphate of zinc. 



Du Bois Reymond, by using connecting pads of filtering-paper, satu- 

 rated with the salt of the connecting liquid, with clay or bladder 

 guards to prevent the muscle from coming in contact with the sulphate 

 of zinc, was enabled to prosecute his investigations without fear of 

 errors arising from the changes in the metallic terminals. At first 

 sight it appears as if this method of experimenting left nothing to be 

 desired. The sulphate of zinc is a good conductor ; the zinc plates 

 produce only a slight action when immersed in the sulphate of zinc, 

 and this action can be readily compensated by a magnet or by a com- 

 pensating current. The muscle can be touched at any part by the pads 

 of filtering-paper or by the clay talons which Du Bois Reymond after- 

 ward used, without danger of injuring the animal tissue. 



It occurred to me, however, from certain experiments upon the elec- 

 tromotive force arising from two liquids of a di-similar chemical nature 



vol. vin. 44 



