64 CHAP. VII. EFFECT OF ELECTRIC STIMULATION 



approach of the secondary to the primary coil, indicated 

 by the higher reading of the scale, gives rise to increasing 

 intensity of stimulation. 



Determination of Latent Period and Time- 

 Relations OF Response 



Experiment 33. Latent period in electric stimulation. — 

 A feeble current was applied for i second to the growing 



region of a bud of Crinum Lily 

 by means of two electrodes, one 

 above and the other below. The 

 record was taken on a moving 

 plate, the magnification employed 

 being 2000 times, and the suc- 

 cessive dots made at intervals 

 of 2 seconds. It was a matter 

 of surprise that the growth of 

 the plant was affected by an 

 intensity of stimulus below even 

 the limit of human perception. 

 As regards the relative sensitive- 

 ness of the plant and the animal, 

 experiments described elsewhere 

 show that the leaf of Mimosa 

 pudica, when in favourable con- 

 dition, responds to an electric 

 stimulus which is one-tenth the 

 minimum intensity that causes perception in a human 

 being. For convenience, I designate the intensity of in- 

 duction current that is barely perceptible to man as the 

 unit of electric stimulus. 



When an intensity of 0-25 unit was applied to the 

 growing organ, it responded to it by a retardation of growth. 

 Inspection of fig. 28 shows that a flexure was induced in 

 the curve in response to the stimulus, denoting retarda- 

 tion of growth. The latent period in this case was 8 seconds. 



Fig. 28. Time-relations of 

 the response of a growing 

 organ to electric stimulus 

 of increasing intensity. 



jMoment of stimulation shown 

 by thick horizontal line. 

 Successive dots at intervals 

 of 2 seconds. (Crinum). 



