84 RESPONSE IN THE LIVING AND NON-LIVING 
the intensity of stimulus increases with the amplitude of 
vibration. Again, keepine the amplitude constant, the 
intensity of stimulus is increased by shortening the wire. 
Hence it will be seen that if the clamp be shifted from 
the balancing point towards A, simultaneous vibration 
of A and B through 90° will now give a resultant upward 
deflection, showing that the A response is now relatively 
stronger. Thus keeping the rest of the circuit untouched, 
merely moving the clamp from the left, past the balanc- 
ing point to the right, we get either a positive, or zero, 
or negative, resultant effect. 
In tin the current of response is from the less to the 
more excited point. In the retina also, we found the 
current of action flowing from the less stimulated to the 
more stimulated, and as that is known as a positive 
response, we shall consider the normal response of tin to 
be in like manner positive. 
Just as the response of retina or nerve, under certain 
molecular conditions, undergoes reversal, the positive 
being then converted into negative, and negative into 
positive, so it will be shown that the response in metal- 
lic wires under certain conditions is found to undergo 
reversal. 
Anomalies of present terminology.—When there is no 
current of injury, a particular current of response can hardly 
be called a negative, or positive, variation. Such nomencla- 
ture is purely arbitrary, and leads, as will be shown, to much 
confusion. A more definite terminology, free from misunder- 
standing, would be, as already said, to regard the current to- 
wards the more stimulated as positive, and that towards the 
less stimulated, in tissue or wire, as negative. 
The stimulated end of tin, say the end 4A, thus becomes 
