The selection of food only one element in sound digestion--Other conditions essential--Times of eating--No stated hours for eating--Five or six hours of interval between meals generally sufficient--But must vary according to circumstances--Habit has much influence--Proper time for breakfast depends on constitution, health, and mode of life--Interval required between breakfast and dinner--best time for dinner--circumstances in which lunch is proper--late dinners considered--their propriety dependent on mode of life--Tea and coffee as a third meal--useful in certain circumstances.--Supper considered.--General rule as to meals.--Nature admits of variety,--illustrations--but requires the observance of principle in our rules. Having in the first part of the present work traced the progress of the food through its successive stages of preparation for becoming a constituent element of the animal frame, and examined the structure and nature of the various organs engaged in digestion, I shall now endeavour to turn the exposition to account, by making it as far as possible subservient to a closer and more rational observance of the laws of digestion, and to a better adaptation of diet and regimen to different ages, sexes, and constitutions, than that which is generally prevalent. I am deeply sensible of the imperfections which will abound in this part of the work; but, at the same time, I am so strongly impressed with the urgent importance of the subject, and with the success which will infallibly attend its further investigation on sound physiological principles, that I consider the likelihood of personal failure to be of very secondary importance, when compared with the benefits which will accrue to society from the exertions of others whose labours may be more profitably directed by an acquaintance with the guiding principles unfolded in these pages. According to the popular notion of dietetics, the selection of the proper kind of food seems to constitute the _only_ condition required for the enjoyment of healthy digestion. Hence medical men are constantly questioned whether this or that article of diet is good or bad for the stomach, while curiosity rarely if ever extends so far as to inquire whether Nature has annexed any other conditions which also it may be expedient to know and to observe. In reality, however, the choice of aliment is but one out of many circumstances which require to be attended to; and it often happens that the same food which is digested with ease when the collateral conditions are fulfilled, will remain for hours on the stomach unaltered when they are neglected. Some of these conditions, therefore, I shall now endeavour to point out. And first, of * * * * *