APPLICATIONS OF THE GRAPHIC METHOD, 189 
not as yet referred to are required to demonstrate the electrical 
condition of muscle. The galvanometer suitable for physio- 
logical experiments is one having very many coils of extreme- 
ly fine wire, and so adapted to indicate the presence of currents 
of slight intensity. 
Tn order that it may be ascertained definitely that the cur- 
rents that deflect the galvanometer needle do not originate out- 
side of the muscle itself, non-polarizable electrodes very care- 
‘fully made must be used, for the contact of ordinary metallic 
electrodes with living tissues suffices of itself to generate an 
electric current, as may be simply illustrated to one’s self by 
placing two coins, one silver and the other copper, in contact 
with the upper and under surfaces of the tongue respectively, 
and meeting in front; a peculiar taste results from the current 
excited, 
The construction of the non-polarizable electrodes common- 
ly employed, and as arranged for use, is diagrammatically rep- 
resented below (Fig. 186). 
Assuming the apparatus for the detection of electrical cur- 
rent in muscle to be in working order, a muscle from one of 
Fic. 186.—Non-polarizable electrodes of Du Bois-Reymond (after Rosenthal). At c, clay tip, 
moistened with saline solution, is laid on muscle. Glass cylinder a@ is filled with stron 
solution of zinc sulphate, a good conductor, by which current is conveyed to amalgamate: 
zinc plate b, and thence to galvanometer. 
the cold-blooded animals, prepared as rapidly and carefully as 
possible, avoiding all contact with foreign bodies, is cut across 
the ends transversely, and placed on pads of bibulous paper 
moistened with physiological (‘60-75 per cent) saline solution. 
The non-polarizable electrodes connected with the galvanome- 
ter are brought in contact with the muscle. What results 
depends on the parts of the muscle that touch the electrodes, 
and is represented diagramatically in Fig. 187. 
It will be observed that the diagram indicates that between 
no current and the strongest obtainable there are all shades of 
