It has been a matter of surprise why tea should be so much sought after by the poorer classes, since by many it is looked on more as a luxury than of use to the human system.  The manner in which it acts, and the cause why it is so much in demand by all classes, is satisfactorily explained by Liebig; and the benefit, therefore, which will be conferred by selling it at a low rate, and thus placing it within the means of all, has at last come to be duly appreciated.  Liebig says, without entering minutely into the medical action of caffeine, theine, &c., it will surely appear a most striking fact, even if we were to deny its influence on the process of secretion, that the substance, with the addition of oxygen and the elements of water, can yield taurine, the nitrogenised compound peculiar to bile:—­

Carbon.    Nitrogen.  Hydrogen.   Oxygen.
1 atom caffeine or theine  =      8        2           5         2
9 atoms water              =     —­       —­           9         9
9 atoms oxygen             =     —­       —­          —­         9
__        __         __        __
= 2 atoms taurine       8        2          14        20
=      2        4           9        10

To see how the action of caffeine, theobromine, theine, &c., may be explained, we must call to mind that the chief constituent of the bile contains only 3.8 per cent. of nitrogen, of which only the half, or 1.9 per cent., belongs to the taurine; bile contains, in its natural state, water and solid matter, in the proportion of ninety parts by weight of the former, to ten of the latter.  If we suppose these ten parts, by weight of solid matter, to be chloric acid, with 3.87 per cent. of nitrogen, then 100 parts of theine would contain 0.171 of nitrogen in the shape of taurine.  Now this quantity is contained in 0.6 parts of theine, or 2 grains 8/10ths of theine can give to an ounce of bile the nitrogen it contains in the form of taurine.

Although an infusion of tea contains no more than the one-tenth of a grain of theine, still, if it contribute in point of fact to the formation of bile, the action even of such a quantity cannot be looked upon as a nullity.  Neither can it be denied, that in the case of an excess of non-azotised food, and a deficiency of motion, which is required to cause the change of matter of the tissues, and thus to yield the nitrogenised product which enters into the composition of the bile, that in such a condition the health may be benefited by the use of compounds which are capable of supplying the place of the nitrogenised substances produced in the healthy state of the body, and essential to the production of an important element of inspiration.  In a chronical sense, and it is this alone which the preceding remarks are intended to show, caffeine, or theine, &c., are, in virtue of their composition, better adapted to this purpose than all nitrogenised vegetable principles.  The action of these substances in ordinary circumstances is not obvious, but it unquestionably exists.  Tea and coffee were originally met with among nations whose diet was chiefly vegetable.