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.
The true remedy for this state of things is, not to turn away in disgust and despair, but to resort to a more rational mode of inquiry—certain that, in proportion as we advance, some useful result will reward our labours. Such, accordingly, has been my aim in the present publication; and if I shall be found to have been even moderately successful in attaining it, I shall rejoice in the confident conviction that others will be led to still more positive and beneficial results. Utility has been my great object throughout. In following what I conceive to be an improved mode of investigation, I have in some instances placed known facts in a new point of view, and deduced from them practical inferences of considerable value and easy application: but beyond this, I lay no claim to originality; and if I have any where used expressions which may seem either to do injustice to others or to arrogate too much credit to myself, it has been entirely without any such design, and, consequently, I will be prompt to acknowledge my error and rectify the involuntary mistake.
In preparing the present volume for the press, I have derived the utmost advantage from a very valuable work by Dr Beaumont, an American writer, which—though faulty in its arrangement, and necessarily defective in many essential particulars—contains an authentic record of some of the most curious and instructive observations which have ever been made on the process of digestion. That excellent and enlightened physiologist had the rare good fortune to meet with a case where an artificial opening into the stomach existed, through which he could see every thing that took place during the progress of healthy digestion; and, with the most disinterested zeal and admirable perseverance, he proceeded to avail himself of the opportunity thus afforded of advancing human knowledge, by engaging the patient, at a heavy expense, to live with him for several years, and become the subject of numerous and carefully conducted experiments. Of the results thus obtained, I have not scrupled to make the freest and most ample use—not from considering them as positively new (for even Dr Beaumont lays little claim to the merit of a discoverer), but because they come before us so entirely freed from the numerous sources of error and doubt which formerly impaired their value, that they can now, for the first time, be safely trusted as practical guides in the science of dietetics. From Dr Beaumont’s work, also, being still inaccessible to the British reader, it is a bare act of justice towards him, and also the best way of fulfilling the objects he had in view, to make its contents known as widely as possible: for wherever they are known, they will be acknowledged to redound to his credit, not less as a man than as a philosopher.
Objections have been stated to several of the repetitions which occur in the following pages. The only apology I have to offer for them is, that I committed them deliberately, because they seemed to me necessary to ensure clearness, and because the intimate manner in which the different functions are connected with each other, sometimes made it impossible to explain one without again referring to the rest. My prime objects being to render the meaning unequivocally plain, and impress the subject deeply upon the reader’s mind, I thought it better to risk in this way the occasional repetition of an important truth, than to leave it in danger of being vaguely apprehended, or its true value unperceived. For these reasons, it is hoped that the fault—if such it is—will be leniently overlooked.
Those who wish to study more fully the subject of Dietetics, will find much useful information in Dr Hodgkin’s “Lectures on the Means of Promoting and Preserving Health;” Professor Dunglison “On the Influence of Atmosphere and Locality, Change of Air and Climate, Seasons, Food, Clothing, Bathing, Exercise, Sleep, Corporeal and Intellectual Pursuits, &c. &c. &c. on Human Health;” Dr Paris “On Diet;” and Dr Kilgour’s “Lectures on the Ordinary Agents of Life, as applicable to Therapeutics and Hygiène.”
CHAPTER I.
GENERAL VIEW OF THE OBJECTS AND LAWS OF NUTRITION.
Waste or loss of substance always attendant on action.—In the vegetable and animal kingdoms waste is greater than in the physical.—Living bodies are distinguished by possessing the power of repairing waste.—Vegetables, being rooted in one place, are always in connexion with their food.—Animals, being obliged to wander, receive their food at intervals into a stomach.—Nutrition most active when growth and waste are greatest.—In vegetables the same causes which increase these processes also stimulate nutrition.—But animals require a monitor to warn then when food is needed.—The sense of Appetite answers this purpose.—The possession of a stomach implies a sense of Appetite to regulate the supplies of food.
Throughout every department of Nature waste is the invariable result of action. Even the minutest change in the relative position of inanimate objects cannot be effected without some loss of substance. So well is this understood, that it is an important aim in mechanics to discover the best means of reducing to the lowest possible degree the waste consequent upon motion. Entirely to prevent it is admitted to be beyond the power of man; for, however nicely parts may be adjusted to each other, however hard and durable their materials, and however smoothly motion may go on, still in the course of time loss of substance becomes evident, and repair and renewal become indispensable to the continuance of the action.
It is thus a recognised fact, or general law of nature, that nothing can act or move without undergoing some change, however trifling in amount. Not even a breath of wind can pass along the surface of the earth without altering in some degree the proportions of the bodies with which it comes into contact; and not a drop of rain can fall upon a stone without carrying away some portion of its substance. The smoothest and most accurately formed wheel, running along the most level and polished railroad, parts with some portion of its substance at every revolution, and in process of time is worn out and requires to be replaced. The same effect is forcibly, though rather ludicrously, exemplified in the great toe of the bronze statue of St Peter at Rome, which in the course of centuries has been worn down to less than half its original size by the successive kisses of the faithful; and I venture to mention it, because it affords one of the best specimens of the operation of a principle, the existence of which, from the imperceptibly small effect of any single act, might otherwise be plausibly denied.
As regards dead or inanimate matter, the destructive influence of action is constantly forced upon our attention by every thing passing around us; and so much human ingenuity is exercised to counteract its effects, that no reflecting person will dispute the universality of its operation. But when we observe shrubs and trees waving in the wind, and animals undergoing violent exertion, for year after year, and yet both continuing to increase in size, we may be inclined, on a superficial view, to regard living bodies as constituting exceptions to the rule. On more careful examination, however, it will appear that waste goes on in living bodies not only without any intermission, but with a rapidity immeasurably beyond that which occurs in inanimate objects. In the vegetable world, for instance, every leaf of a tree is incessantly pouring out some portion of its fluids, and every flower forming its own fruit and seed, speedily to be separated from and lost to its parent stem; thus causing in a few months an extent of waste many hundred times greater than what occurs in the same lapse of time after the tree is cut down, and all its living operations are at a close. The same thing holds true in the animal kingdom. So long as life continues, a copious exhalation from the skin, the lungs, the bowels, and the kidneys, goes on without a moment’s intermission; and not a movement can be performed which does not at least partially increase the velocity of the circulation, and add something to the general waste. In this way, during violent exertion several ounces of the fluids of the body are sometimes thrown out by perspiration in a very few minutes; whereas, after life is extinguished, all the excretions cease, and waste is limited to that which results from ordinary chemical decomposition.