CHAP. IV. §. I. IN THE STOMACH AND INTESTINES. 33 



and a dilute solution of muriate of soda, and con- 

 sider the two metals as forming the terminations 

 of the electrodes of the galvanometer, one of zinc 

 and the other of platinum, instead of having two 

 platinum electrodes as heretofore. When the elec- 

 trodes 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 con- 

 tact 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 



D 



