Fig. 93.—‘Molecular Arrest’ by the Action of ‘poison’
In each, curves to the left show the normal response, curve to the right shows the effect of poison. In (a) the arrest is evidenced by prolongation of period of recovery. In (b) there is no recovery.
(1) The effect of these reagents is not only to increase or diminish the height of the response-curve, but also to modify the time relations. By the action of some the latent period is diminished, others produce a prolongation of the period of recovery. Some curious effects produced by the change of time relations have been noticed in the account given of diphasic variation (see [p. 113]).
(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 development 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.
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.