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166 that causes perception in a human being. For convenience I shall designate the intensity of electric shock that is barely perceptible to us as the unit shock. When an intensity of 25 unit was applied to the growing organ, it responded to it by a retardation of growth. Inspection of Fig. 61 shows

that there is a flexure induced in the curve in response to stimulus, the flattening of the curve denoting retardation of growth. The latent period, in this case, is 6 seconds. The normal rate was restored after f) minutes. The intensity of shocK was next raised from 0*25 unit to one unit. The second recoril shows that the latent period is reduced to 4 Fig. 61.-1 ime-ieiations of response seconds, and a relatively oi growing organ to electric stimulus greater retardation of growth

of increasing intensities applied at the ^^^ induced by the aCtion of short horizontal lines. Successive dots

at intervals of 2 seconds. the Stronger stimulus. The

recovery of the normal rate was eft'ected after the longer period of 10 minutes. I took one more record, the intensity being three units. The latent period was now reduced to 1 second, and the induced retardation was so great as to eft'ect a temporary arrest of growth.

TABLE X. — TIME-RELATIONS OF RESrONSIVE GROWTH-VARIATION UNDER ELECTRIC SHOCK {Crhium).

Intensity of stimulus.

Latent period.

Normal rate. Retarded rate.

0"2o unit.

1

3

6 seconds.

4

1

0-62 fi per sec.

0-62

0-62

49 /A per sec. 0-25 Temporary arrest of growth.