542 ADDENDUM. 



circuit of a thermopile, which circuit also included a ' currentless ' 

 nerve (i. e. a nerve to which the leading off electrodes were applied 

 at equipotential points) the hydrostatic pressure required to zero 

 the electrometer, i. e. to bring back the column of mercury to the 

 position which it occupied when * short circuited,' accurately 

 indicated the electromotive force of the pile. In other words, 

 it made no difference as regards the reading of the electrometer 

 whether the polarised nerve were in or out of the circuit. The form 

 of Fleischl's experiment, of which the result is regarded by him as 

 inconsistent with all that has been advanced on the subject of 

 nerve-polarisation on either side, may be described as follows : 



The line e k E k n k f k' represents a circuit in which are included 

 at n a nerve (by equipotential contacts) and at e a capillary 

 electrometer, furnished with an arrangement by which the pressure 

 of mercury in the capillary can be regulated and measured, k k' 

 and k k' represent keys or bridges by which either nerve or 

 electrometer can be short-circuited at will. At E an electromotive 

 source is introduced into the circuit, which, as above stated, was 

 in "Professor Fleischl's experiments a thermopile, of which one 

 set of junctions was heated by a small Bunsen. The experiment 

 consisted in first measuring the electromotive force of E with 

 k k' closed and k k' open, then closing k k' and opening k tf so as 

 to lead the current of E through the nerve, and finally opening 

 k k' so as to obtain a second measurement. It was found that the 

 two measurements were identical. It was therefore evident that 

 in the intrapolar tract, the effect of the polarisation of the nerve 

 was not such as to balance the opposed polarisation of the electro- 

 meter. When the experiment was varied by substituting for the 

 nerve a non-living polarisable arrangement a voltameter of the 

 kind known as ' Wollaston's points ' (platinum wires fused into 

 glass tubes so as to cover all but their tips) the polarisation of the 

 points evidenced itself by a diminution of the reading of the 

 electrometer which persisted for some hours. 



It is evident therefore that the polarisation of a nerve is not 

 quite the same as the polarisation of a voltameter. As to what 

 the difference consists in, Hermann has sought to enlighten us 



