DIVERTING CYLINDERS. 



181 



Apart from the foct 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. Diveuting cylinders as used by E. du Bois Reymond- 



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 divertins^ arch should touch the 

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

 other form of diverting apparatus, invented by du 

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

 conducting currents to the body under examination in 

 cases where it is important to avoid electrical polari- 

 sation. These, which are usually called unpolaris- 

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



