84 RESPONSE IN THE LIVING AND NON-LIVING 



the intensity of stimulus increases with the amplitude of 

 vibration. Again, keeping 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 A, thus becomes 



