THE SIGNS OF LIFE 



[LECT. 



Here is a nerve-muscle preparation, the nerve of which is 

 laid across electrodes that are connected with the keyboard 

 and galvanometer. There can also be led into the keyboard, 



Anode Kathode 



FlG. 40. Nerve-muscle preparation ; to demonstrate the muscular contractions 

 associated with the positive anodic after-current in nerve. 



by means of a double key, a strong battery-current which is to 

 traverse the nerve in an ascending direction as figured (the 

 galvanometer meanwhile being plugged). During the passage 

 of the constant current, the muscle remains quiescent, but when 

 I break the current, the muscle, as you see, contracts, and will 

 contract for a longer or shorter period. Immediately after 

 breaking the battery current, I unplug the galvanometer, when 

 you witness a strong and permanent positive deflection, signifi- 

 cant of an action-current in the nerve of the same direction 

 as that of the previous battery-current. The deflection is not 

 absolutely permanent, it is gradually falling, the muscle will not 

 remain indefinitely contracted, it will relax sooner or later ; the 

 positive current in the nerve, and the contraction of the muscle, 

 are associated effects of a state of local irritation or action in the 

 previously anodic region of the nerve. You know that the 

 current from an active to an inactive spot of nerve runs in the 

 nerve from active to inactive (in the galvanometer from 

 inactive to active, the latter pole being therefore called nega- 

 tive), and that the active spot acts like the zinc of a voltaic 

 couple is in brief a zincative spot. Therefore you know from 

 the direction of this after-current that the active spot from 

 which the irritation to the muscle proceeds is post-anodic as 

 to its source in the nerve itself. 



59. Locality of reaction. Polar inequalities of effect have 



