i 4 6 RESPONSE IN THE LIVING AND NON-LIVING 



(2) The effect produced by a chemical reagent 

 depends to some extent on the previous condition of 

 the wire. 



(3) A certain time is required for the full develop- 

 ment of the effect. With some reagents the full effect 

 takes place almost instantaneously, while with others 

 the effect takes place slowly. Again the effect may 

 with time reach a maximum, after which there may be 

 a slight decline. 



(a) (b) (c) 



FIG. 94. OPPOSITE EFFECTS OF SMALL AND LARGE DOSES (TIN) 



(a) is the normal response ; (b) is the stimulating action of small dose of 

 potash (3 parts in 1,000) ; (c) is the abolition of response with a stronger 

 dose (3 parts in 100). 



(4) The after-effects of the reagents may be transitory 

 or persistent ; that is to say, in some cases the removal 

 of the reagent causes the responses to revert to the 

 normal, while in others the effect persists even after 

 the removal of all traces of the reagent. 



Opposite effects of large and small doses. There 

 remains a very curious phenomenon, known not only 



