“A third series, of four experiments, was also made during four fasts of thirty-six hours each—­two with water only, and two with tea to drink.

“In the following particulars, all the three series so entirely coincide, that the conclusions will be set down as general deductions from the whole.

“Tea, in ordinary doses, has not any effect on the amount of carbonic acid expired, the frequency of the respirations, or of the pulse.”

Obviously, then, it is not with reference to the heat-producing function that we can look upon tea as in any sense a nutriment; and if it causes no saving of carbon, its effects must be sought in checking some other waste, or in the less consumption of nitrogen.  The pulse, and hence the respiration, are unaltered; for the two great processes of circulation and aeration of the blood are interdependent functions, and have, in health, a definite ratio of activity one with the other.  As a nervous stimulant, tea in excess will, as we all know, produce an exaltation of the action of the heart, amounting in some persons to a painful and irregular palpitation.  No such result seems to follow its moderate use.

“The loss by perspiration is limited by tea.”  This seems, at first, contrary to common experience, as the sensible perspiration produced by several cups of warm tea is a familiar fact to all tea-drinkers.  That this effect is wholly owing to the warmth of the mixture, it being drunk usually in hot infusion or decoction, was pointed out long since by Cullen.  Tea limits perspiration, perhaps, by the astringent action of the tannin which it contains,—­of which more hereafter.  What is saved by limiting perspiration?  Water, largely; carbonic acid, in considerable amount; ammonia (a nitrogenized substance;) salts of soda, potash and lime, and a trace of iron, all in quantities minute, to be sure, but to be counted in the aggregate of arrest of metamorphosis.

But the great fact which establishes tea as an arrester of the change of tissue is, that its use diminishes remarkably the amount of nitrogen thrown off by the excretions, specially destined to remove that element, when in excess, from the system.  “We have before called attention to the fact, that an indispensable component of plastic food, by which alone the tissues are repaired, is nitrogen.  By a chemico-vital process, nitrogen builds up and is incorporated in the tissues.  Nitrogen, again, is one of the resulting components of the change of tissue.  This element forms a large part of the effete particles which are rejected on accumulation from such change or waste.  That a less amount is excreted by the tea-drinker, when similar quantities are ingested, the weight and plumpness of the body remaining undiminished the while, is proof of the slower change of tissue which takes place under the modifying influence of tea.  The importance of this effect we shall presently see.