Page:Collected Physical Papers.djvu/293

Rh of chemical reagents. Drugs profoundly modify the response of living substances; the effects of which may be classified under three classes, some acting as stimulants, others as depressors, and yet others again as poisons, by which response is permanently abolished. Amongst the last may be mentioned mercuric chloride, oxalic acid and others. Again, drugs which in large doses become poisons, may, when applied in small quantities, act as stimulants.

It may be thought that to these phenomena, inorganic matter could offer no parallel. For they involve possibilities which have been regarded as exclusively physiological. Accustomed in the animal to find the responsive condition transformed into the irresponsive state at the moment of death, we look on this sequence as peculiar to the world of the living. And on this fact is based the supreme test by which physical and physiological phenomena are differentiated. That only can be called living which is capable of dying, we say, and death can be accelerated by the administration of poison. The sign of life as given by the electric pulses then wanes, till it ceases altogether. Molecular immobility—the rigor of death—supervenes, and that which was living is no longer alive.

Is it credible that we might, in like manner, kill inorganic response by the administration of poison? Could we by this means induce a condition of immobility in metals, so that, under its influence, their electric responses should wane and die out altogether?

Before we attempt the action of poisons let us study the exciting effect of stimulants. You observe the normal extent of response under successive uniform stimuli applied to one wire of the cell. I now add a few