168 SECONDARY ELECTROMOTIVE PHENOMENA IN 



and water with salt solution. The internal polarisation in this case 

 is stronger but more evanescent in character, the external weaker 

 but more lasting-, which explains the slight negative first deflection, 

 followed by a principal deflection which is positive. 



All the fresh animal tissues which I have examined behave 

 between two saline pads like a water-pad. A piece of rib, costal 

 cartilage, sinew, elastic tissue, frog's skin, human skin, pieces of 

 lung, liver, spleen, rabbit's kidneys, and lastly, muscles and nerves 

 they all assume positive external polarisation which sums itself 

 algebraically with internal negative polarisation. Under circum- 

 stances otherwise the same, the latter is more strongly developed 

 the greater the length of the portion of tissue through which 

 the current is passed l . If animal tissues are exposed to a current 

 between the usual pads soaked with a solution of sulphate of zinc, 

 and covered with a layer of clay, kneaded with a * physiological ' 

 solution of common salt (i. e. O'6 per cent.), the external polarisation 

 is very little marked 2 . But it is advisable, in order to avoid errors 

 in investigation of the internal polarisation of muscles and nerves, 

 not to lead off the secondary electromotive polarisation current by 

 means of the same pads, clay tips, &c. by which the primary 

 current has been led through it, or at least not to lose sight of the 

 fact that if this arrangement becomes necessary under certain cir- 

 cumstances, polarisation at the boundaries of the dissimilar electro- 

 lytes may come into play. 



5. Further Continuation of Preliminary Studies. External 

 and Internal Polarisation of moist porous bodies. 



When I reached this point I thought I knew enough of what 

 takes place during the passage of a current through a series of moist 

 porous bodies, to enable me safely to continue my researches on the 

 secondary electromotive phenomena of muscles and nerves. But I 

 found myself greatly mistaken. After I had made numerous experi- 

 ments of this kind I discovered a new source of error, by which my 

 work up to this time was rendered, if not useless, at least inade- 

 quate. This was what I have called secondary resistance ' of 

 moist porous bodies, which I now made the subject of a long 



1 Op. cit. vol. i. pp. 1-12: 'Uber Polarisation an der Grenze ungleichartiger 

 Elektrolyte' (July 17, 1856). 

 3 Op. cit. vol. ii. pp. 189 ff. 



