produced not merely on photographic plates, but also on sheets of ordinary metals (p. 213). Molecular impression produce in other ways than by light is seen in the inductoscripts and in the development of pressure marks.
Recurrent photographic reversals are produced under continued action of light similar to those under continuous mechanical stimulation (p. 215).
Owing to tendency towards self-recovery, the resulting effect does not solely depend on the total quantity of incident light, but also on the time-rate of illumination. Hence for the same duration of exposure, the photographic effects of intermittent and continuous illuminations are not the same (p. 217).
D. The Similarity of Response of Inorganic and Living Substances
A molecular upset is produced in inorganic substances by the impact of stimuli, electrical or mechanical. The response is recorded by methods of conductivity and electromotive variations.
In inorganic receivers for electric radiation, continuous stimulation induces fatigue which is removed after a period of rest. Prolonged rest, however, makes the receiver inert, and the lost responsivity is then only restored after a period of stimulation (p. 353). These characteristics are similar to those in the response of living substance.
Successive stimuli of equal intensity give rise to uniform inorganic responses. Superposition of stimuli causes incomplete or complete "tetanus" according to slow or quick frequency of stimulation (p. 256).
