CHAP. VIII. MUSCULAR AND NERVOUS TISSUES. 89 



First, They may depend upon the changes which 

 occur during nutrition. 



Secondly, They may depend, also, upon the hetero- 

 geneity of the parts ; (including under this term the 

 action of the platinum electrodes, viz. the catalytic 

 action or combining power of platinum upon the 

 moist animal substances in contact with its surface ;) 

 and also, 



Thirdly, Upon a polarized condition of the nerve or 

 muscular fibre. 



Fourthly, That this polamaed condition of the fibre 

 is produced and maintained by nutrition. And, 



Fifthly, That the circumstances under which the 

 current may be produced may resemble, in one 

 instance, those arising from the changes which occur 

 in the decomposing cell of a voltaic circle ; and in 

 the other, those that arise from the action of a 

 charged Ley den jar. In the latter case, the current 

 being due to the polarized condition of the fibre ; 

 in the former, to the changes which occur during 

 nutrition. 



