This being the case, then, can we, their descendants, maintain that we are arrived so nearly at perfection as to leave no room for corresponding improvement in our day? My conviction is so much the reverse, that it seems to me certain that our onward progress will continue through generations yet unborn, with the same steadiness as it has done through generations long since gathered to their fathers; and that every attempt made to render man better acquainted with the laws of his own constitution, and thereby provide him with fixed and better principles of action, will exert a positive and decided influence on the progress of the race, proportioned in extent to the _truth_, clearness, and general applicability of the views which are unfolded. On such considerations do I ground my hope that the present volume, notwithstanding its numerous defects, will (in so far as it really embodies truths of practical importance) contribute in its own limited sphere to the general end. The real cause of the little regard paid to dietetic rules--and it is of consequence to remark it--is not so much indifference to their influence, or even the absolute want of valuable information, as the faulty manner in which the subject is usually considered. In many of our best works, _the relation subsisting between the human body on the one hand, and the qualities of alimentary substances on the other_, is altogether lost sight of, although it is the only solid principle on which their proper adaptation to each other can be based. In this manner, while the attention is carefully directed to the consideration of the abstract qualities of the different kinds of aliment, little or no regard is paid to the relation in which they stand to the individual constitution, as modified by age, sex, season, and circumstances, or to the observance of the fundamental laws of digestion. And hence, although these conditions are not unfrequently of much greater importance to the general health than even the right selection of food, yet, when indigestion arises from neglecting them, the food alone is blamed, and erroneous conclusions are drawn, by relying on which, upon future occasions, we may easily be led into still more serious mistakes. It is, indeed, from being left in this way without any guiding principle to direct their experience, and test the accuracy of the precepts laid down to them for the regulation of their conduct, that many persons begin by being bewildered by the numerous discrepancies which they meet with between facts and doctrine, between counsel and experience,--and end by becoming entirely sceptical on the subject of all dietetic rules whatever, and regarding them as mere theoretical effusions, based on fancy, and undeserving of a moment’s consideration.