IV PREFACE. 



of this volume ; and secondly, that by the mechanical method 

 it is possible to explore the condition of the nerve in the 

 ' intra-polar ' region, i.e. in that part of its course which lies 

 between the inflow and outflow of the current. It may be stated 

 generally that the observations of Tigerstedt made by so different 

 a method, while they extend those of Pflliger, afford additional 

 evidence of their accuracy, the only difference between them 

 being that the state of diminished excitability at the cathode 

 after opening of the current is found not to be so marked when 

 tested mechanically as when tested electrically. 



The second paper contains the results of a new investigation of 

 the * Law of Contraction,' with special reference to the conditions 

 which determine the state of excitation that occurs at the anode 

 at the moment that a current led through a motor nerve is 

 broken. The author shows that these conditions correspond 

 with those which produce ordinary negative polarisation in the 

 nerve, that is, a state of the nerve in which, if the seat of outflow 

 of the current be investigated immediately after the circuit is 

 broken, it is found to be negative to all other parts ; and he 

 thinks that this correspondence is so close, that the two concomi- 

 tant phenomena, viz. the contraction of the muscle and the polari- 

 sation of its nerve, must have the same cause. He is thus led to 

 regard the make and break contractions as phenomena which are 

 alike produced by the closing of a current, but which differ from 

 each other as regards the way in which this current itself origin- 

 ates. This research should be read along with that of Grlitzner 

 (No. 4) on the same subject, who by different experimental 

 methods has arrived at the same explanation of the anodic con- 

 traction. He finds that by far the greater number of the known 

 instances in which the phenomenon can be experimentally in- 

 vestigated admit of more complete and satisfactory explanation 

 as resulting from negative polarisation than on Pfliiger's theory. 

 The special cases which he has investigated are (i) that in 

 which the anodic excitation produced by breaking a current 

 which is led through a nerve in a direction opposed to the nerve- 

 current, is found to be dependent on certain complicated but 



