142 RESPONSE IN THE LIVING AND NON-LIVING 
shows the effect of the same reagent on platinum 
(fie. 90). 
Action of depressants.—Certain other reagents, again, 
produce an opposite effect. That is to say, they 
diminish the intensity of response. The record given 
on the next page (fig. 91) shows the depressing action 
of 10 per cent. solution of KBr on tin. 

Before 4p After 
Fra. 90.—Strimunatine Action oF Na,CO, on PLatinum 
Effect of ‘ poison.’—Living tissues are killed, and their 
electric responses are at the same time abolished by the 
action of poisons. It is very curious that various chemical 
reagents are similarly effective in killing the response 
of metals. I give below a record (fig. 92) to show how 
oxalic acid abolishes the response. The depressive 
effect of this reagent is so great that a strength of one 
part in 10,000 is often sufficient to produce complete 
