142 RESPONSE IN THE LIVING AND NON-LIVING 



shows the effect of the same reagent on platinum 

 (fig. 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 f After 

 FIG. 90. STIMULATING ACTION OF Na./30 3 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 



