It has been alleged by a friendly critic of the first edition, that the author is too sanguine in expecting that the mere communication of knowledge will suffice to alter the habits of the race, and that, although the information conveyed in the present volume may be turned to account by third parties--by mothers and nurses, for example--“yet with respect to the direct effect upon eaters,” slender results must be anticipated. “The world,” it is wittily added, “will read, admire, and applaud Dr Combe on Digestion and Dietetics, and then go on in its usual way _eating what it likes, and digesting what it can_.” The Author, however, never entertained the hope that his work would immediately produce the slightest perceptible change in the general practices of society, or that many healthy men of mature age and confirmed habits would forsake their accustomed regimen merely because it was shewn to be at variance with the laws of Nature. But as human conduct is in some measure influenced by knowledge, he is still confident enough to believe, that, among valetudinarians and the young of both sexes, whose habits are not formed, and numbers of whom err as much from ignorance as from the force of passion, many may be found who will be glad to obtain the guidance of knowledge and principle in the regulation of their mode of life; and that even many parents, who may not have resolution enough to forsake mischievous indulgences to which they have long been accustomed, may nevertheless be anxious to avail themselves of any assistance on which they can depend for the better bringing up of their children. If in these expectations he is not too sanguine, the future advantage to the race from the present diffusion of dietetic knowledge is as certain, and almost as encouraging, as if its effects were instantaneous on both old and young. In the march of human improvement, months and years count but as moments. The _men_ of to-day will soon have acted their part, and give place to those who are now with youthful energy adding to their knowledge, and throwing off a portion of the prejudices of their fathers. They in their turn will speedily be succeeded by their children, and the discoveries of the one generation will thus become the established and influential truths of the next. Each individual change in the habits of society may be so slow and minute as at the moment to escape our notice, but it is not on that account the less real. Nobody who compares the coarse feeding and riotous convivialities of our forefathers, at the beginning of last century, with the more refined and temperate habits of the present day, will think of denying that a prodigious step has been made in the interval even with respect to eating and drinking, which the critic seems to consider as so much beyond the influence of reason. And yet, if we take any single year of the whole century, we shall be unable to particularize any marked reformation which took place within its limits.