146 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) (d) (c) 
Fic. 94.—Oprostre Errects or Smati anp Larce Doses (Try) 
(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 
