448 ELECTRO-PHYSIOLOGY CHAP. 



upon this point it is advisable to cite the essential data in re 

 polarisation phenomena. 



Let a still-living piece of Malapterurus organ, which, as we 

 have seen, is usually isoelectric, be laid across unpolarisable 

 electrodes, serving simultaneously to lead in and lead off; a 

 special contrivance sends in a battery current of definite intensity 

 and duration, and immediately after (when the polarising circuit 

 is opened) closes the galvanometer circuit, as has already been 

 described for muscle. The organ-preparation will then, as a rule, 

 have become temporarily electromotive (polarised), and this at 

 low current-density invariably in the direction of a negative 

 after -current heterodromous to the exciting current. This 

 negative polarisation occurs in Malapterurus in loth directions 

 (homodromous and heterodromous with the discharge) in equal 

 strength, and grows in density and duration, with the product, to 

 still undetermined proportions. Positive polarisation invariably 

 occurs first, as in nerve and muscle, at high densities of current, 

 and is most apparent (du Bois-Eeymond) with brief currents, its 

 intensity increasing with the duration of the exciting current less 

 rapidly than that of negative polarisation. The greater intensity 

 of positive polarisation in the direction of the discharge (also 

 observed by du Bois-Eeymond) is very striking. " The current 

 from head to tail exhibits strong positive polarisation under the 

 same conditions in which that from tail to head gives negative 

 polarisation" (4 d, p. 206). Obviously wherever there is simul- 

 taneous appearance of both polarisations, the actual after- current 

 is the algebraic sum of the two opposite actions, and it is easy to 

 understand that there might also, under certain conditions, be 

 diphasic (first negative, then positive) deflections, or oscillations 

 of the magnet. 



Sachs made analogous observations on strips of Gymnotus 

 organ, with the inessential difference that polarisation is, in 

 this case, invariably negative at first, while du Bois-Eeymond 

 occasionally obtained pure positive effects on the Malapterurus 

 organ under certain conditions, which must, however, be re- 

 ferred solely to the lesser density of the currents employed by 

 Sachs. (Du Bois-Eeymond sent current from 20-30 Groves 

 through strips of Malapterurus that were hardly -g- sq. cm. in 

 diameter.) 



Du Bois-Eeymond subsequently found occasion in Berlin to 



