GENERAL SURVEY AND CONCLUSION 187 
is also shown sometimes after continuous stimulation, 
not only in animal tissues, but also in metals (fig. 115). 
Modified response.—In the case of nerve we saw 
that the normal response, which is negative, sometimes 
becomes reversed in sign, i.e. positive, when the 
specimen is stale. In retina again the normal positive 
response is converted into negative under the same 
conditions. Similarly, we found that a plant when 
withering often shows a positive instead of the 
A M 

3efore After Before After 
Fic. 116.—Mopririep ApnormaL Response 1n (A) Nerve and (M) Meran 
CONVERTED INTO NorMAL, AFTER CONTINUOUS STIMULATION 

(A) is the record for nerve (recording galvanometer not being dead-beat shows 
after-oscillation) ; the abnormal ‘up’ is converted into normal ‘ down’ after 
continuous stimulation. (M) is the record for metal, the abnormal ‘ down’ 
being converted into normal ‘up’ after like stimulation. 
usual negative response (fig. 28). On nearing the death- 
point, also by subjection to extremes of temperature, 
the same reversal of response is occasionally observed 
in plants. This reversal of response due to peculiar 
molecular modification was also seen in metals. 
But these modified responses usually become normal 
when the specimen is subjected to stimulation either 
strong or long continued (fig. 116). 
