PREFACE. IX 



to the ' intra-polar ' region, but also to extra-polar parts in its 

 neighbourhood. Hermann is accordingly led to regard all 

 secondary electromotive phenomena as resulting from the inter- 

 ference of the excitatory change which occurs at the anode in 

 consequence of the opening of the current, with ordinary galvanic 

 polarisation, it being understood that the physical change always 

 anticipates the vital one as regards the order of its occurrence ; 

 so that whenever the conditions (strong current and short 

 closure) are such as to enable these two antagonistic influences 

 to manifest themselves together, the process consists of a more 

 transitory physical effect, which is followed by a more lasting 

 physiological one. 



If the views of Hermann and Hering are accepted, the reader 

 will see that the form given by Tigerstedt and Griitzner to their 

 theory as to the essential nature of the opening contraction must 

 be modified. Tigerstedt assumes that at the break of a current, 

 the anode becomes, in consequence of negative polarisation, 

 virtually a cathode, an assumption which takes no account of 

 the facts of positive polarisation. On 'this point the reader will 

 compare with advantage du Bois' criticism of Tigerstedt in his 

 sixteenth paragraph, with that of Hermann in the paragraph 

 which precedes his conclusion. 



If it is true that * positive polarisation ' of a nerve or of a 

 muscle is in reality a purely physiological, or, in other words, an 

 excitatory effect of the leading through it of a voltaic current, it 

 becomes of interest to enquire what is the relation of the elec- 

 trical after-effects so fully studied by du Bois-Reymond, Hering, 

 and Hermann, to the more mechanical effects which form the 

 subject of the first part of this series. In general it is, as every 

 physiologist knows, extremely difficult to demonstrate in detail 

 the correlation which undoubtedly exists between the electro- 

 tonus of Pfluger, and the galvanoscopic phenomena which were 

 originally investigated by du Bois and treated of by him under 

 the same title. The chief reason of the difficulty lies in the 

 circumstance that until recently it has been possible to investi- 

 gate the former only in muscle, the latter only in nerve. But 



