ANIMAL ELECTRICITY. LECTURE If. 4 1 



alterations such as those exemplified in fios. 26 and 

 27 are not ambiguous. 



With a dead-beat magnet, which moves sluggishly, 

 as if plunged in a sticky fluid, matters are quite 

 different. The time it takes to pass from one posi- 

 tion of rest to another is its " risincr " or " fallincr " time. 

 Any brief impulse that it may receive is lost ; and 

 while it is falling back to a position of rest at the 

 termination of an effect, it will not show whether 

 the after-state is positive or negative to the previous 

 state. It is only if the after-state is very prolonged, 

 in comparison with the falling time, fifteen seconds, 

 that the magnet will indicate its presence, and then 

 we practically only get signs of the after-state from 

 the end of the falling time onw^ards. 



Thus, however, the two kinds of magnet supple- 

 ment each other as witnesses ; both indicate the state 

 durino- excitation, the swino^ino- mao-net indicates the 

 state immediately after excitation, the dead-beat 

 magnet the state during a later period after excitation. 



Let us now turn to perhaps more familiar matters, 

 and make use of this apparatus to test the effects upon 

 nerve, of alcohol, soda water and tobacco smoke. 



A nerve is lying upon its electrodes in the moist 

 chamber (fig. 10). The wash-bottle is half full of fresh 

 soda water, all the keys are closed, the galvanometer 

 spot is at zero. I open K, (from the nerve) and K3 (to 

 the galvanometer) and the spot moves half across the 



