Science almost always finds some foundation in fact for popular prejudices.  For years, men have continued wasting their substance on coffee and tea, insisting that they strengthened as well as comforted them, in spite of the warnings of the sanitarian, who looked on them solely as stimulants or sedatives, and of the economist, who bewailed their extravagant cost.

Physiology, relying on organic chemistry, has at least justified by experiment the choice of the civilized world.  Coffee and tea had been regarded by the physiologist and the physician as stimulants of the nervous system, and to a less extent and secondarily of the circulation, and that was all.  To fulfil this object, and to answer the endless craving for habitual excitants of the cerebral functions, they had been admitted reluctantly to the diet of their patients, rather as necessary evils than as positive goods.  It was reserved for the all-searching German mind to discover their better qualities; and it is only within the last five years, that the self-sacrificing experiments of Dr. Boecker of Bonn, and of Dr. Julius Lehmann, have raised them to their proper place in dietetics, as “Accessory Foods.”  This term, which we borrow from the remarkable work on “Digestion and its Derangements,” by Dr. Thomas K. Chambers, of London, is only the slightest of the many obligations which we hasten to acknowledge ourselves under to this author, as will appear from citations in the course of this article.

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.