Johnston (‘Chemistry of Common Life’) closely following Liebig, and referring to the researches of Lehmann, says: ‘_The waste of the body is lessened by the introduction of theine into the stomach—that is, by the use of tea._ And if the waste be lessened, the necessity for food to repair it will be lessened in an equal proportion. In other words, by the consumption of a certain quantity of tea, the health and strength of the body will be maintained in an equal degree upon a smaller quantity of ordinary food. _Tea, therefore, saves food_—stands to a certain extent in the place of food—while, at the same time, it soothes the body and enlivens the mind.’ He proceeds to say that ‘in the old and infirm it serves also another purpose. In the life of most persons a period arrives when the stomach no longer digests enough of the ordinary elements of food to make up for the natural daily waste of the bodily substance. The size and weight of the body, therefore, begin to diminish more or less perceptibly. At this period _tea comes in as a medicine to arrest the waste_, to keep the body from falling away so fast, and thus to enable the less energetic powers of digestion still to supply as much as is needed to repair the wear and tear of the solid tissues.’ No wonder, therefore, says he, ‘_that the aged female, who has barely enough income to buy what are called the common necessaries of life, should yet spend a portion of her small gains in purchasing her ounce of tea. She can live quite as well on less common food when she takes her tea along with it_; while she feels lighter at the same time, more cheerful, and fitter for her work, because of the indulgence.’ (The italics are my own for comparison with those that follow.) All this is based upon the researches of Lehmann and others, who measured the work of the vital furnace by the quantity of ashes produced—the urea and phosphoric acid excreted. But there is also another method of measuring the same, that of collecting the expired breath and determining the quantity of carbonic acid given off by combustion. This method is imperfect, inasmuch as it only measures a portion of the carbonic acid which is given off. The skin is also a respiratory organ, co-operating with the lungs in evolving carbonic acid. Dr. Edward Smith adopted the method of measuring the respired carbonic acid only. His results were first published in ‘The Philosophical Transactions’ of 1859, and again in Chapter XXXV. of his volume on ‘Food,’ International Scientific Series.