240 Electricity and Galvanism* 



galvanometer, will not be visible to all. I have here a glass tube 

 closed at one end by an animal membrane — a piece of bladder. I 

 fill it with a weak solution of soda, and immerse it in a glass vessel 

 containing some diluted acid. The soda and acid are gradually 

 combining through the walls of the membrane. I now plunge a 

 plate of platinum into the acid, and connect the wire fixed to it to 

 one screw of the galvanometer ; fixing the wire of a second plate to 

 the other screw, I plunge it into the alkali ; the needles of the galva- 

 nometer instantly start into motion, and traverse a considerable arc, 

 pointing out the existence of a current of positive electricity from 

 the acid to the alkali through the conducting wires. Now, with the 

 exception of the stomach and ccecum, the whole extent of the mucous 

 membrane is bathed with an alkaline mucous fluid, and the external 

 covering of the body, the skin, is as constantly exhaling an acid 

 fluid, except in the axillary and perhaps pubic regions. The mass 

 of the animal frame is thus placed between two great envelopes, the 

 one alkaline, and the other acid, meeting only at the mouth, nostrils, 

 and anus. This arrangement has been shown by Donne to be 

 quite competent to the evolution of electricity, and accordingly he 

 found that if a platinum plate connected with the galvanometer be 

 held in the mouth, whilst a second be passed against the moist 

 perspiring surface of the body, the needles will instantly traverse, 

 just as they did in the experiment I have just shown with acid and 

 alkali. The current thus detected by Donne at once explains the 

 cause and confirms the accuracy of the celebrated experiment of 

 Professor Aldini, to which I have already drawn attention. I refer 

 to that in which he excited convulsions in a frog by holding its 

 foot in the moistened hand, and allowing the sciatic nerve to touch 

 the tongue. His curious experiment with the head of an ox admits 

 of a similar explanation. 



A remarkably energetic current also can be thus detected when the 

 platinum plates are plunged, one into the acid contents of the stomach 

 of an animal, the other into the alkaline secretion of the liver. This 

 gastro-hepatic current is of so very remarkable a character that it will 

 once more occupy our attention. 



Within the last few months, the results of some researches of 

 Liebig have rendered it very probable that a large proportion of the 



