The potatoe again, whose introduction has added many millions to our population, derives its origin from a small and hitter root, which grows wild in Chili and at Monte Video 1. These few instances may suffice to answer the object for which they were introduced: the reader will find many others in the Introduction to my Pharmacologia2. If, however, any of my readers should be still sceptical upon the subject of such metamorphoses, let them visit the fairy bowers of horticulture, and they will there perceive that her magic wand has not only converted the tough, coriaceous covering of the almond into the soft and melting flesh of the peach, but that, by her spells, the sour sloe has ripened into the delicious plum, and the austere crab of our woods into the golden pippin; that this, again, has been made to sport in almost endless variety, emulating in beauty of form and colour, in exuberance of fertility, and in richness of flavour, the rarer productions of Marnier regions and more propitious climates.

1 A work was published some time since by a Mr. Newton, entitled "A Return to Nature:" in which the author advocates the necessity of vegetable diet, and of the abandonment of food which Nature never intended for our use. I confess, that upon opening the work, I was not a little amused by the sentence which first met my eye: - "Our drink is distilled water, having a still expressly for this purpose in our back-kitchen "!! Art versus Nature would have been a more appropriate title for such a production.

6. If cultivation can ever be said to have left the transformation of vegetables imperfect, the genius of cookery is certainly entitled to the merit of having completed it: for, whatever traces of natural qualities may have remained, they are undoubtedly obliterated during their passage through her potent alembic. It has been observed, that the useful object of cookery is to render aliments agreeable to the senses, and of easy digestion; in short, to spare the stomach a drudgery which can be more easily performed by a spit or stew-pan - that of loosening the texture, or softening the fibres of the food; and which are essential preliminaries to its digestion. A no less important effect is produced by rendering it more palatable; for it is a fact, which I shall have to consider on a future occasion, that the gratification which attends a favourite meal is, in itself, a specific stimulus to the organs of digestion, especially in weak and debilitated habits.

1 See Pharinacologia, edit. 8. p. 112. 2 Ibid. p. 114.

7. Experience can alone supply the want of instinct; and, unless we assume this as the basis of all our inquiries upon the subject of diet, our theories, however refined, and supported by chemical and physiological researches, will prove but Will-o'-th'-wisps, to lead us astray into numerous difficulties and embarrassments. Experience, for instance, dearly-bought experience, has taught us that headach, flatulency, hypochondriasis, and a thousand nameless ills, have arisen from the too-prevailing fashion of loading our tables with that host of French entremets, and fiors-d'osuvres, which have so unfortunately usurped the roast-beef of old England. The theorists, in the true spirit of philosophical refinement, laugh at our terrors: they admit, to be sure, that the man who eats round the table, "ab ovo usque ad mala," is a terrific glutton, but that, after all, he has only eaten words; for, eat as he may, he can only eat animal matter, vegetable matter, and condiment, either cooked by the heat of water or by that of fire, figure or disfigure, serve, arrange, flavour, or adorn them as you please.

There is not a physician of any practical knowledge who cannot, at once, refute such a doctrine; 7 every nurse knows, from experience, that certain mixtures produce deleterious compounds in the stomach, although the chemist may perhaps fail in explaining their nature, or the theory of their formation. What would such a reasoner say, if he were invited to a repast, and were presented only with charcoal and water? would he be reconciled to his fare by being told that his discontent was founded on a mere delusion? that the difference between them and the richest vegetable viands was merely ideal, an affair of words, as in either case he would only swallow oxygen, hydrogen, and carbon? And yet the presumption in such a case would not be more violent, nor would the argument be less tenable, than that by which the chemist attempts to defend the innocence of a practice which converts our refreshments into burdens, and our food into poison. It is an ancient observation that, "under some circumstances, words become things;" and, in the instance before us, the words of the sophist are certainly things to the stomach.

To those who question the value of dietetic regulations in the cure of disease, I have only to observe, that they may as well deny the utility of the medical art altogether, and assert that, in all disorders of function, Nature is sufficiently powerful to rectify and cure them, without the intervention of art: unless this be granted, it is absurd to say that beneficial impressions may not be made as well through the medium of the materia alimentaria, as through that of the materia medica; or, to borrow the language of Dr, Arbuthnot, that what Ave take daily by pounds must be, at least, as important as what we take seldom, and only by grains or tea-spoonsful; but the truth is that the practitioner of the present clay, animated by an increasing confidence in the multiplied resources of chemistry, is unfortunately disposed to undervalue the therapeutic influence of diet; he feels with pride the full quiver at his shoulders, and he disdains the use of familiar weapons.

8. Those who have read my work on Pharmacology will easily discover the train of research by which my mind has been led, from the study of the operation of medicines, to that of the digestion of aliment; while those who are acquainted with the various works on dietetics will readily admit, that an ample apology may be found for giving to the public another volume on that subject.

9. Before the subject of dietetics can be systematically considered, or the principles upon which disease may be prevented or cured by an appropriate diet, can be properly understood, or profitably applied, the reader must be made acquainted with the complicated machinery by which Nature extracts blood from food. The various processes engaged in this wonderful transmutation are expressed by the comprehensive term digestion, although this word is sometimes employed, in a more limited sense, to denote only those preparatory changes which the food undergoes in the stomach. Mr. Abernethy would appear to use the term according to this latter acceptation, for he says, - "Digestion takes place in the stomach, chylification in the small intestines, and a third process, hitherto undenominated, is performed in the large intestines." The reader, however, of this work is to understand that, by Digestion, is meant the whole series of functions from mastication to sanguification; for in truth the changes which take place during the act of respiration are as essential to nutrition as chymification, or the farther elaboration of the food into chyle.

The relation of a tale which has been so often told may, perhaps, appear to many as superfluous: I must, however, remark, that every author is conventionally allowed to state the theme of his discussion in his own language, and the advantages which have hitherto attended the indulgence sufficiently sanction its continuance.