If we neglect the preliminary negative portion under sub-minimal stimulus, the curve of excitation under increasing photic stimulation obeys what is known as Weber's law. This is equally true of modes of stimulation other than that of light as is seen in figure 130 of the contractile effect of continued electric stimulus on growth; the excitatory effect is also seen to reach a limit. Weber's law is applicable for a limited range of stimulation. For the quantitative relation fails in the region of sub-minimal stimulus, where the physiological reaction is _qualitatively_ different, namely expansion instead of contraction. This holds good even in the case of animal tissues, for here also my recent experiments show that two opposite reactions--expansion and contraction--take place under stimulus, and that a very feeble stimulus tends to induce expansion instead of contraction. The responsive reaction of a kitten under gentle caressing strokes must be _qualitatively_ different from that of a blow. The psychological effects under the two treatments evidently differ qualitatively rather than quantitatively.[19] [19] "It has been argued by James that the feeling does not cause, but is caused by the bodily expression.... Münsterberg concludes that the feeling of agreeableness is the mental accompaniment and outcome of reflexly produced movements of extension, and disagreeableness of the movement of flexion." Schäfer--Text Book of Physiology, Vol. II, p. 975 (1900). SUMMARY. The excitation curve exhibits a slow ascent in the first part; in the second part the gradient is steep, indicating rapid rise in excitation; in the third part it is uniform; and in the last part the curve rounds off and the rate of ascent becomes very small. The susceptibility for excitation is feeble at the beginning; it increases very rapidly with increasing stimulus; finally it undergoes a fall, increase of stimulus inducing no further enhancement of excitation. In a complete phototropic curve the first part is negative; this is due to the physiological expansion induced by sub-minimal stimulus. The curve then crosses the abscissa upwards, and the positive curvature reaches a maximum. This is followed by neutralisation and reversal into negative; the curve crosses the zero line and proceeds in the negative direction. Weber's law is not applicable for the entire range of stimulation. The quantitative relation fails in the region of sub-minimal stimulus, where the physiological reaction is _qualitatively_ different. XXXIII.--THE TRANSMITTED EFFECT OF PHOTIC STIMULATION _By_ SIR J. C. BOSE, _Assisted by_ JYOTIPRAKASH SIRCAR, M.B.