The labors of earlier physiologists and chemists, as Carpenter, Liebig, and Paget, had resulted in the classification of nutritive substances under different heads, according to the purposes they served in the physical economy. Perhaps the most convenient, though not an unexceptionable division, is into the Saccharine, Oleaginous, Albuminous, and Gelatinous groups. The first includes those substances analogous in composition to sugar, being chemically composed of hydrogen, carbon, and oxygen. Such are starch, gum, cellulose, and so forth, which are almost identical in their ultimate composition, and admit of ready conversion into sugar by a simple process of vital chemistry. The oleaginous group comprises all oily matters, which are even purer hydro-carbons than the first-mentioned class. The third, or albuminous group, includes all substances closely allied to albumen, and hence containing a large proportion of nitrogen in addition to the other three elements. The last group consists also of nitrogenized substances, which resemble gelatine in many of their characteristics. The first two groups are called non-azotized, as they contain no nitrogen; the last two, azotized, containing nitrogen. "All articles of food that are to be employed in the production of heat must contain a larger proportion of hydrogen than is sufficient to form water with the oxygen that they contain, and none are appropriate for the maintenance of any tissues (except the adipose) unless they contain nitrogen." Hence the obvious restriction of the first two classes to the heat-producing function, and of the last two (or azotized) to the reparation of the tissues.
We have, then, the two natural divisions of calorifacient and plastic foods: the one adapted to sustain the heat of the body, and enable us to maintain a temperature independent of that of the medium we may be in; the other to build up, repair, and preserve in their natural proportions the various tissues, as the muscular, fibrous, osseous, or nervous, which compose our frames. These two kinds of food we must have in due proportion and quantity in order to live. Neither the animal nor the vegetable kingdom furnishes the one to the exclusion of the other. We derive our supplies of each from both. More than this, we consume and appropriate certain incidental elements, which find their place and use in the healthy system. Iron floats in our blood, sulphur lies hidden in the hair and nails, phosphorus scintillates unseen in the brain, lime compacts our bones, and fluorine sets the enamelled edges of our teeth. At least one-third of all the known chemical elements exist in some part of the human economy, and are taken into the stomach hidden in our various articles of food. This would seem enough for Nature's requirements. It is enough for all the brute creation. As men, and as thinkers, we need something more.
In all the lower orders of creation the normal state is preserved. Health is the rule, and sickness the rare exception. Demand and supply are exactly balanced. The contraction of the voluntary muscles, and the expenditure of nervous power consequent on locomotion, the temperate use of the five senses, and the quiet, regular performance of the great organic processes, limit the life and the waste of the creature. But when the brain expands in the dome-like cranium of the human being, a new and incessant call is made on the reparative forces. The nervous system has its demands increased a hundred-fold. We think, and we exhaust; we scheme, imagine, study, worry, and enjoy, and proportionately we waste.
In the rude and primitive nations this holds good much less than among civilized people. Yet even among them, the faculties whose possession involves this loss have been ever exercised to repair it by artificial means. In the busy life of to-day how much more is this the case! Overworked brains and stomachs, underworked muscles and limbs, soon derange the balance of supply and demand. We waste faster than enfeebled digestion can well repair. We feel always a little depressed; we restore the equilibrium temporarily by stimulation,—some with alcohol and tobacco, others with coffee and tea. Now it is to these last means of supply that the name has been given of "accessory foods."
"Accessories are those by whose use the moulting and renewing (that is, the metamorphosis) of the organic structures are modified, so as best to accommodate themselves to required circumstances. They may be subdivided into those which arrest and those which increase metamorphosis." It is under the former class that are placed alcohol, sugar, coffee, and tea. Again, says Dr. Chambers,—"Not satisfied with the bare necessaries," (the common varieties of plastic and calorifacient food,) "we find that our species chiefly are inclined by a soi-disant instinct to feed on a variety of articles the use of which cannot be explained as above; they cannot be found in the organism; they cannot, apparently, without complete disorganization, be employed to build up the body. These may be considered as extra diet, or called accessory foods….. These are what man does not want, if the protracting from day to day his residence on earth be the sole object of his feeding. He could live without them, grow without them, think, after a fashion, without them. A baby does. Would he be wise to try and imitate it?
"Thus, there is no question but that easily assimilable brown meat is the proper food for those whose muscular system is subjected to the waste arising from hard exercise; and if plenty of it is to be got, and the digestive organs are in sufficiently good order to absorb enough to supply the demand, it completely covers the deficiency. Water, under these circumstances, is the best drink; and a 'total abstainer,' with plenty of fresh meat, strong exercise, and a vigorous digestion, will probably equal anybody in muscular development. But should the digestion not be in such a typical condition, should the exercise be oversevere and the victuals deficient, then the waste must be limited by some arrester of metamorphosis; if it is not, the system suffers, and the man is what is called 'overworked.'…. Intellectual labor also exercises the demand for food, and at the same time, unfortunately, injures the assimilating organs; so that, unless a judicious diet is employed, waste occurs which cannot be replaced."
Waste, we may be told, is life, and the rapidity of change marks the activity of the vital processes. True, if each particle consumed is at once and adequately replaced. Beyond that point, let the balance once tend to over-consumption, and we approach the confines of decay. Birds live more and faster than men, and insects probably most of all; yet many of the latter are ephemeral.
Every-day experience had long pointed to the recurring coincidence, that, of the annual victims of pulmonary consumption, few were to be found among the habitual consumers of ardent spirits. Science volunteered the explanation, that alcohol supplied a hydro-carbonaceous nutriment similar to that furnished by the cod-liver oil, which, serving as fuel, spared the wasting of the tissues, just in proportion to its own consumption and assimilation. Other aid it was supposed to lend, by stimulating the function of nutrition to renewed energy. Later investigations have proved that it exercises a yet more important influence as an arrester of metamorphosis. It was on arriving at this conclusion, that Dr. Böcker was led to institute a series of careful experiments to determine the influence of water on the physical economy, and the real value of salt, sugar, coffee, tea, and other condiments, as articles of food. "The experimenter appears to have used the utmost precision, and details so conscientiously the mode adopted of making his estimates, that additional knowledge may perhaps alter the conclusions drawn, but can never diminish the value of the experiments." They are not open to the objections of mistaken sensations, and honest, though ludicrous, misapprehension of fallible symptoms, to which the testing of drugs homeopathically is liable, and of which another instance has just occurred in London, in the "proving" of the new medicinal agent, gonoine. They rather resemble in accuracy a quantitative, as well as a qualitative, analysis. We will cite first the experiments on tea, and quote from the interesting narrative of Dr. Chambers.
"After Dr. Böcker had determined by some preliminary trials what quantity of food and drink was just enough to satiate his appetite without causing loss of weight to his body,—that is to say, was sufficient to cover exactly the necessary outgoings of the organism,—he proceeded to special experiments, in which, during periods of twenty-four hours, he took the amount of victuals ascertained by the former trials.
"The first set of the first series of experiments consists of seven observations, of twenty-four hours' duration each, in the months of July and August, with three barely sufficient meals per diem, in quantities as nearly equal each day as could be managed, and only spring-water to drink. The second set comprises the same number of observations in August, September, and October, under similar circumstances, except that infusion of tea, drunk cold, was taken instead of plain water.