364 
PEOFESSOE MATTEUCCI’S ELECTEO-PHYSIOLOGICAL EESEAECHES. 
sign of current was indicated by tire galvanometer, the plates of zinc were amalgamated 
afresh, the cushions were carefully washed by agitating the glasses in a solution of sulphate 
of zinc, and the solution in the glasses was renewed. These preliminary arrangements 
ha\dng been made, the piece of muscle or nerve, the electromotor power of which was to be 
examined, was laid on a flat handle-shaped piece of gutta percha, and brought into contact 
with the two extremities of the cushions. After a certain number of experiments, 
between each of Avhich it is necessary to ascertain that no current is developed when 
the cushions are put in immediate contact, it frequently happened that a certain altera- 
tion began to manifest itself ; so that before the experiment could be continued, the 
zinc plates had to be amalgamated afresh, the cushions washed, and the solution in 
the glasses renewed as above described. 
I have latterly succeeded in introducing some useful modiflcations in this method of 
experimenting, by means of which much trouble is saved, and the experiments are so 
simplifled as to be executed rapidly, and at the same time with exactness. 
Instead of two glasses, I now employ two tubes bent in the form of a U, one branch 
or arm of which is much larger than the other, and terminates like a funnel furnished 
with a broad flattened beak. These tubes are nearly fllled with an amalgam of zinc, 
so dense as to be almost solid. A copper wire united to the galvanometer is inserted 
into the smaller branch of each tube and im- 
mersed in the amalgam. The large wide-mouthed 
branches of the tubes are filled up to the brim 
with the usual saturated neutral solution of zinc, 
so that the liquid extends in a very thin stratum 
over their flattened beaks. It is easy to lay on 
these beaks a single stratum of unsized paper, which becomes instantly soaked, and can 
be renewed without the least difficulty. Thanks to this improvement in the way of ope- 
rating, I have been able to carry on a series of experiments for months together without 
any sign of the currents which used so frequently to be produced between the liquids in 
the glasses ; there is no longer any need of amalgamating afresh the zinc plates, and 
when the solution in the tube requires renewal the operation is quickly performed. 
I shall describe, finally, an important part of the method pursued in these researches 
for comparing the electromotor power of difierent animal parts. This method (already 
well known, and which I have always followed in my electro-physiological researches*) 
is independent of the resistance of the elements themselves, and of the influence of time 
on animal structures ; it consists in opposing two electromotor elements, and in obseiuing 
the direction and intensity of the differential currents thus obtained. The tvm 
elements are laid on the gutta-percha holder, so as to place the two poles of the same 
name in contact. If, for instance, a comparison is to be made between the electromotor 
power of two pieces of frogs’ thighs, a double pile is formed by bringing into contact the 
two transverse sections and closing the circuit, or vice versa by touching the corresponding 
* Philosophical Transactions, 1845. 
