252 Mb BAXTER, ON ORGANIC POLARITY. 



pare the results with another class of phenomena, viz. with those actions which take place in a 

 voltaic circle where decomposition is effected. 



It will be better to confine our attention to the actions which take place in the exciting 

 cell of a voltaic circle where the power originates, and withdraw our minds for the present 

 entirely from the changes which take place in the decomposing cell of the battery where polar 

 decompositions are effected : the principal object being to ascertain whether, during the 

 decomposition of a compound, or during the separation of an acid from an alkali, the same 

 effects are produced upon the galvanometer as occurs during the combination of an acid with 

 an alkali. 



Let us take an elementary circle, zinc, platinum, and a dilute solution of muriate of soda, 

 and consider the two metals as forming the terminations of the electrodes of the galva- 

 nometer, one of zinc and the other of platinum, instead of having two platinum electrodes as 

 heretofore. When the electrodes are dipped into the solution, the actions which take place 

 are the following : the muriate of soda is decomposed by the attraction of the zinc for the 

 chlorine or muriatic acid, whilst the soda is evolved on the surface of the platinum ; now 

 under these circumstances the platinum electrode, in contact with the soda, is positive to 

 the other, and, according to common phraseology, the direction of the current is in the same 

 direction as the cation (the alkaline compound, the soda) is supposed to travel. Here then 

 is a case of decomposition, a separation of an acid from an alkali, effected by chemical agency, 

 and the electrode in contact with the alkali is positive to the other in contact with the 

 acid ; the effect being contrary to that observed during the combination of an acid with 

 an alkali, as has been just shewn. Let us now compare the results which occur in the 

 animal with those which take place in the voltaic circle. When the electrode is brought 

 into contact with the venous blood, it is positive to the other in contact with the secreting 

 surface of the intestine; if it be now supposed that the blood is alkaline, and there is 

 every ground for so doing, the electrode in contact with the blood is exactly similar to 

 that in contact with the alkali in the voltaic circle ; but instead of the secreted product com- 

 bining with the other electrode, as the acid does in the voltaic circle, it passes away. In the 

 animal the current may be supposed to be dependent upon the decomposition — if I may 

 so term it — of the arterial blood, being as it were separated into its two elements, the secreted 

 product and venous blood, just as the muriate of soda is decomposed and separated into its 

 two elements, muriatic acid and soda. 



At present, it may be remarked, that no opinion as to the mode in which the 

 secretions are effected is being given ; I am only endeavouring to ascertain now what 

 does occur, and to what class of phenomena these actions, those of secretion, bear the 

 greatest resemblance. This subject will again come under our consideration. 



Before proceeding to shew that in other organs there exists the same manifestation of cur- 

 rent force during secretion, I cannot omit noticing the opinion that Woli,aston entertained 

 in regard to the question now under consideration, and shall therefore quote his own words : 

 " At the time," says Wollaston*, " when Mr Davy first communicated to me his 



• Loe. cit. 



