So much for the net results of the stimulant action of tobacco. So far we have travelled on firm ground, and we have not found much to countenance Mr. Parton's view of the subject. But now some curious inquirer may ask, what _is_ this stimulant action? What is the physiological expression for it, reduced to its lowest terms? Here we must keep still, or else venture upon ground that is very unfamiliar and somewhat hypothetical. There is no help for it; for we cannot yet give the physiological expression for unstimulated nervous action, reduced to its lowest terms. We know what kind of work nerves perform, but how they perform it we can as yet only guess. Nor, as far as the practical bearings of our subject are concerned, does it matter whether this abstruse point be settled or not. Still, even upon this dark subject recent research has thrown some gleams of light. A nerve-centre is a place where force is liberated by the lapse of the chemically-unstable nerve-molecules into a state of relative stability.[22] To raise them to their previous unstable state, thereby enabling them to fall again and liberate more force, is the function of food. Now our own hypothesis is, that tobacco and other narcotic stimulants enable force to be liberated by the isomeric transformation of the highly complex nerve-molecules, which retain in the process their state of relative instability, and are thus left competent to send forth a second discharge of force without the aid of food. [22] We fear that this explanation will be rather unintelligible to the general reader. But it is hardly practicable for us to insert here a disquisition on physiological chemistry. Those who are familiar with modern physiology will readily catch our meaning. Those who are not may skip, if they choose, this parenthetical paragraph. In support of this hypothesis we have the well-known fact that tobacco, like tea, coffee, alcohol and coca, universally retards organic waste. These substances effect this result in all the tissues, and more especially may they be expected to accomplish it in nervous tissue, where their action is so conspicuously manifest. Thus is explained the familiar action of narcotic-stimulants in relieving weariness. Weariness, in its origin, is either muscular or nervous. It implies a diminution--owing to failing nutrition--of the total amount of contractile or of nervous force in the organism; and it shows that the weary person must either go to sleep or eat something. Now every one knows how a cup of tea, a glass of wine, or a cigar, dispels weariness. Of the three agents, tobacco is perhaps the most efficacious, and it can produce its effect in only one way--namely, by economizing nervous force, and arresting the disintegration of tissue.