It would be difficult to overestimate the practical importance of these results.  They raise coffee and tea from the rank of stimulants to that of food,—­from idle luxuries to real agents of support and lengthening of life.  Henceforth the economist can hear of their increasing consumption without a regret.  The poor may indulge in them, not as extravagant enjoyments, but practical goods.  The cup of tea, which is the sole luxury of their scanty meal, lessens the need for more solid food; it satisfies the stomach, while it gladdens the heart.  It saves them, too, the waste of those nitrogenized articles of food which require so much labor and forethought to procure.  The flesh meats and the cereals, which contain the largest amounts of this requisite of organic life, are always the dearest articles of consumption.  Certainly it is not as positive nutriment that we recommend the use of coffee and tea; for although they contain a relatively large amount of nitrogen, that supply can be better taken in solid food.  Their benefit is two-fold.  While they save more than enough of the waste of tissue to justify their use as economical beverages, they supply a need of the nervous system of no small importance.  They cheer, refresh, and console.  They thus fill a place in the wants of humanity which common articles of food cannot, inasmuch as they satisfy the cravings of the spirit as well as of the flesh.

We have before attempted to show that the human race is liable to a peculiar and constant waste from the development of the nervous system, and that the body has to answer for the labor of the mind.  At first thought, we shall find it difficult to appreciate the endless vigilance and activity of the brain.  Like the other organisms which possess a proper nervous system, man carries on the common organic processes of life with a regularity and unfailing accuracy which seem to verge on the mechanical forces, or to be, at least, automatic.  All habitual voluntary acts by repetition become almost automatic, or require no perceptibly distinct impulse of the will.  When we emerge from this necessary field of labor, we come to those functions peculiar to the proper brain.  Here all is continual action.  Thought, imagination, will, the conflicting passions, language, and even articulation, claim their first impulse from the nervous centre.  The idlest reverie, as well as the most profound study, taxes the brain.  That distinguishing attribute of man can almost never rest.  In sleep, to be sure, we find a seeming exception.  Then only its inferior portion remains necessarily at work to supervise the breathing function.  Yet we know that we have often dreamed,—­while we do not know how often we fail to recall our dreams.  The duality of the cerebrum may also furnish a means of rest in all trivial mental acts.  Still, the great demands of the mind upon the nervous tissues remain.  And it is these losses which may be peculiarly supplied by the nervous stimulants.  Such are coffee