1901.] on the Response of Inorganic Matter to Stimulus. 



619 



the conductor or optic nerve, free from injury. Finally, just as the 

 galvanometer will fail to detect a current if its suspension-thread be 

 broken by rough usuage, so, after a violent blow, the brain will no 

 longer perceive, though the terminal organ, the retina, and the con- 

 necting optic nerve may be intact. 



So we see that stimulus evokes an electrical change also, in a 

 living tissue. I shall now proceed to enter into some detail re- 

 garding this electric mode of response. 



The various complicated phenomena of electric 

 Hydraulic response may perhaps be rendered more easily 

 Model. intelligible by means of a hydraulic model 



(I, Fig. 2). Imagine an indiarubber pipe full 

 of water, whose two ends A and B are at the same level. There 

 would then be no current in the side or canal-pipe P. But sup- 

 pose the end A is struck, a wave of disturbance will travel from A 

 towards B. At a given moment the level at the A end will be raised, 



Fig. 2. — Hydraulic Models. 



and the side tube will exhibit a current from A to B (Z 1 , Fig. 2); but, 

 after a little while, A will subside to the normal level, the disturb- 

 ance having meanwhile travelled to B, whose level will now be 

 raised. The current in the side tube will now be reversed in direc- 

 tion (Z 11 , Fig. 2). A disturbing shock applied to one end of A B will 

 thus produce a diphasic variation, and a float or indicator in the side 

 pipe will exhibit this effect by alternate movement, first to one side 

 and then to the other. If, however, the rate of transmission of dis- 

 turbance be very great, then the indicator will fail to show any move- 

 ment, inasmuch as it will be acted on by two equal and opposite 

 impulses almost simultaneously. 



1. To make the indicator exhibit the effect of shock in producing 

 disturbance of level, we may proceed as follows. We may clamp 

 the pipe in the middle at C (see m, Fig. 2), so that when one end is 

 struck the disturbance may not proceed to the other end, the clamp 



