DIVERTING CYLINDERS. 



181 



Apart from the fact that the insertion of the animal 

 substances between the pads cannot always be con- 

 veniently managed, it is impossible to bring individual 

 points of the substance into contact with the pads. This 

 does not matter at all when the iso-electric curves run 

 parallel to each other, as in the case described in 2, 

 on the outer surface of the cylinder. In such cases it 

 is always sufficient to apply the sharp edges of the clay 

 discs to the surface in such a way that all the points 

 which come in contact with these edges belong to the 

 same iso-electric curve. But even in observations on 



FIG. 45. DIVERTING CYLINDERS AS USED BY E. t>u Bois REYMOXP. 



the surfaces of the ends of the cylinder the case is dif- 

 ferent. Here the iso-electric curves form concentric 

 circles. In such cases it is absolutely necessary to 

 carry out with somewhat greater accuracy the theoretic 

 condition that the diverting arch should touch the 

 conductor which is to be examined at two points. An- 

 other form of diverting apparatus, invented by du 

 Bois-Reymond, is used both for this purpose and for 

 conducting currents to the body under examination in 

 cases w T here it is important to avoid electrical polari- 

 sation. These, which are usually called unpolaris- 

 able electrodes, are represented in fig. 45. The glass 



