V/ OA/^ THE PHYSIOLOGY OF DIGESTION CONSIDERED WITH RELATION TO THE PRINCIPLES OF DIETETICS. 1/ BY ANDREW COMBE, M. D. FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS OF EDINBURGH, AND PHYSICIAN IN ORDINARY TO THEIR MAJESTIES THE KING AND QUEEN OF THE BELGIANS. " Nor is it left arbitrary, at the will and pleasure of every man, to do as he list; after the dictates of a depraved humor and extravagant phancy, to liye at what rate he pleaseth; but every one is bound to observe the Injunctions and Law of Nature, upon the penalty of forfeiting their health, strength, and liberty—the true and long enjoy- ment of themselves." Mainwayringe. f: FIRST AMERICAN EDITION. R% BOSTON: MARSH, CAPEN & LYON. 1836. WX Entered according to Act of Congress, in the year 1836, by Marsh, Capen & Lyon, in the Clerk's Office of the District Court of Massachusetts. Printed by William A. Hall & Co. PREFACE. The present volume is essentially a continuation of the work first published about two years ago, under the title of " The Principles of Physiology applied to the Preservation of Health and to the Improvement of Phys- ical and Mental Education ;" and its object is the same —namely, to lay before the public a plain and intelligi- ble description of the structure and uses of some of the ore important organs of the human body, and to show ow information of this kind may be usefully applied in practical life. In " The Principles of Physiology," the structure and functions of the skin, muscles, bones, lungs, and ner- vous system, the laws or conditions of their healthy ac- tion, and the unsuspected origin of many of their diseases in infringements of these laws, were explained in suc- cession and at considerable length ; and the means by which their health and efficiency might best be secured were pointed out. It was stated that, in selecting these organs as subjects for discussion, I had been guided by the desire to notice in preference those functions which IV PREFACE. are most influential in their operation on the general system, and at the same time least familiarly known ; and that, if the attempt to convey the requisite infor- mation in a manner suited to the general reader should prove successful, I would afterwards prepare a similar account of others, in the right understanding and man- agement of which our interest is not less deeply involv- ed, but in regard to which much ignorance continues nevertheless to prevail, even among the most liberally educated classes of society. The numerous proofs which I received of the utility of my former work, not only from professional and lit- erary journals, but also from individuals previously un- known to me,—many of them guardians and instructed of youth, speaking from personal experience,—together with the rapid sale of three editions (the last consisting of 3000 copies) in two years, soon completely satisfied me that I had neither been deceived as to the real im- portance of physiological knowledge to the general pub- lic, nor been altogether unsuccessful in the method of conveying it. Thus encouraged, accordingly, I cheer- fully resumed my labors, and began the preparation of the treatise now submitted to the indulgent considera- tion of the reader. The matters discussed on the present occasion relate chiefly to the function of Digestion and the principles of Dietetics ; and in selecting them I have been guided by the same principle as before. It may, at first sight, be doubted whether I have not exceeded proper bounds in thus dedicating a whole volume to the consideration of a single subject; but the more we consider the real PREFACE. V complication of the function of Digestion,—the exten- sive influence which it exercises at every period of life over the whole of the bodily organization—the degree to which its morbid derangements undermine health, happiness, and social usefulness, and especially the share which they have in the production of scrofulous and consumptive as well as of nervous and mental affec- tions,—we shall become more and more convinced of the deep practical interest which attaches to a minute acquaintance with the laws by which it is regulated. In infancy, errors in diet, and derangement of the digestive organs, are admitted to be the principal causes of the striking mortality which occurs in that period of life. In youth and maturity, the same influence is recognised, not only in the numerous forms of disease directly trace- able to that origin, but also in the universal practice of referring every obscure or anomalous disorder to de- rangement of the stomach or bowels. Hence, loo, the interest which has always been felt by the public in the perusal of books on Dietetics and Indigestion ; and hence the prevalent custom of using purgatives as rem- edies for every disorder, very often with good, but not unfrequently with most injurious effects. Numerous and popular, however, as writings on Die- tetics have been, and excellent as are many of the pre- cepts which have been handed down by them from the earliest ages, sanctioned by the warm approval of every successive generation, it is singular how very trifling their influence has been, and continues to be, in altering the habits of those to whom they are addressed. In a genernl way, we all acknowledge that diet is a power- VI PRF.FACE. ful agent in modifying the animal economy; yet, from our conduct, it might justly be inferred, that we either regarded it as totally devoid of influence, or remained in utter ignorance of its mode of operation, being left to the guidance of chance alone, or of notions picked up at random, often at variance with reason, and, it may be> in contradiction even with our own daily experi- ence. The cause of this extraordinary anomaly—and it is of consequence to remark it—seems to be, not so much the absolute want of valuable information, as the faulty manner in which the subject is usually consider- ed. In many of our best works, the relation subsisting between the human body on the one hand, and the qual- ities of the alimentary substances on the other, as the only solid principle on which their proper adaptation to each other can be based, is altogether lost sight of; so that, while the attention is carefully directed to the con- sideration 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 mod- ified by age, sex, season, and circumstances, or the ob- servance 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 PREFACE. VII guiding principle to direct their experience, and test the accuracy of the precepts laid down to them for the regu- lation of their conduct, that many persons begin by be- ing 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 labors. Such, accordingly, has been my aim in the present pub- lication ; and if I shall be found to have been even mod- erately successful in attaining it, I shall rejoice in the confident conviction that others will be led to still more positive and beneficial results. Utility, and not novelty, has been my great object throughout; and, therefore, although in some instances I have perhaps regarded known facts in a new point of view, and deduced from them practical inferences of considerable value, I lay no claim to any farther originality, except such as is impli- ed in the adoption of what I conceive to be an improv- ed mode of investigation ; 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, consequent- ly, I will be prompt to acknowledge my error and rec- tify the involuntary mistake. In preparing the present volume for the press, I have viii PREFACE. derived the utmost advantage from a very valuable work by Dr Beaumont, an American writer, which, though scarcely at all known in this country, contains an au- thentic record of some of the most curious and instruc- tive obsesvations 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 exist- ed, through which he could see every thing that took place during the progress of healthy digestion ; and, with the most disinterested zeal and admirable perse- verance, he proceeded to avail himself of the opportu- nity 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 nu- merous and carefully conducted experiments. Of the results thus obtained, 1 have not scrupled to make the freest and most ample use ; both because they illustrate almost every point of importance connected with diges- tion, and because, from Dr Beaumont's work being still inaccessible to the British reader, it is a bare act of justice towards him, and also the best way of fulfill- ing 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. In the course of these pages the reader will occasion- ally meet with repetitions, which he may, perhaps with justice, think unnecessary. The only apology I have to offer for them is, that the intimate manner in which the different functions are connected with each other, PREFACE. IX sometimes made it impossible to explain one without referring to the rest; and also that 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 occasional repetition of an im- portant truth, than to leave it in danger of being vaguely apprehended ,or its enunciation in any degree obscure. 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, Exer- cise, 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 Hygiene." Brussels, April, 1836. CONTENTS. PART I. PHYSIOLOGY OF DIGESTION. CHAPTER I. INTRODUCTORY remarks. 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 connection 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 them 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. 1-10 CHAPTER IL THE APPETITES OF HUNGER AND THIRST. Hunger and Thirst, what they are----Generally referred to the stomach and throat, but perceived by the brain—Proofs XII CONTENTS. and illustrations Exciting causes of hunger—Common theo- ries unsatisfactory—Hunger sympathetic of the state of the body as well as of the stomach—Uses of appetite—Relation between waste and appetite—Its practical importance—Con- sequences of overlooking it illustrated by analogy of the whole animal kingdom—Disease from acting in opposition to this relation—Effect of exercise on appetite explained—Diseased appetite—Thirst—Seat of Thirst—Circumstances in which it is most felt—Extraordinary effects of injection of water into the veins in cholera—Uses of thirst, and rules for gratifying CHAPTER III. MASTICATION, INSALIVATION, AND DEGLUTITION. Mastication—The teeth—Teeth, being adapted to the kind of food, vary at different ages and in different animals—Teeth classed and described—Vitality of teeth and its advantages— Causes of disease in teeth—means of protection—Insalivation and its uses—Gratification of taste in mastication—Degluti- tion........... 36-52 CHAPTER IV. ORGANS OF DIGESTION—THE STOMACH—THE GASTRIC JUICE. Surprising power of digestion—Variety of sources of food—All structures, however different, formed from the same blood— General view of digestion, chymification, chylification, san- guification, nutrition—The stomach in polypes, in quadru- peds, and in man—Its position, size, and complexity, in differ- ent animals—Its structure; its peritoneal, muscular, and vil- lous coats; and uses of each—Its nerves and blood-vessels, their nature, origins, and uses—The former the medium of communication between the brain and stomach—Their rela- CONTENTS. Xiii lion to undigested food—Animals not conscious of what goes on in the stomach—Advantages of this arrangement—the gas- tric juice the grand agent in digestion—Its origin and na- ture—Singular case of gunshot wound making a permanent opening into the stomach—Instructive experiments made by Dr Beaumont—Important results......53-100 CHAPTER V. THEORY AND LAWS OF DIGESTION. Different theories of Digestion—Concoction—Fermentation -Putrefaction—Trituration—Chemical solution—Conditions or laws of digestion—Influence of gastric juice—Experiments illustrative of its solvent power—Its mode of action on differ- ent kinds of aliment—beef, milk, eggs, soups, &c.—Influence of temperature—Heat of about 100° essential to digestion— Gentle and continued agitation necessary—Action of stom- ach in admitting food—Uses of its muscular motion—Gas- tric juice acts not only on the surface of the mass, but on every particle which it touches—Digestibility of different kinds of food—Table of results—Animal food most digestible—Fari- naceous next—Vegetables and soups least digestible—Organs of digestion simple in proportion to concentration of nutri- ment—Digestibility depends on adaptation of food to gastric juice more than on analogy of composition—Illustrations— No increase of temperature during digestion—Dr Beau- mont's summary of inferences......101-142 CHAPTER VI. CHYLIFICATION, AND THE ORGANS CONCERNED IN IT. Chylification—Not well known—Organs concerned in it—The intestinal canal—Its general structure—Peritoneal coat—Me- sentery—Muscular coat—Uses of these—Air in intestines— XIV CONTENTS. Uses of—Mucous coat—Analogous to skin—The seat of ex- cretion and absorption—Mucous glands—absorbent vessels— Course of chyle towards the heart—Nerves of mucous coat— Action of bowels explained—Individual structure of intestines —The Duodenum—Jejunum—and Illeum—Liver and pan- creas concerned in chylification—Their situation and uses— Bile, its origin and uses—The pancreas—Its juice—The je- junum described—the Ileum—Ccecum—Colon, and Rectum Peristaltic motion of bowels—Aids to it—Digestion of vege- tables begins in stomach but often finished in the bowels—Il- lustration from the horse—Confirmation by Dupuytren. 143-174 PART II. THE PPINCIPLES OF DIETETICS VIEWED IN RELATION TO THE LAWS OF DIGESTION. CHAPTER I. TIMES OF EATING. 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 gen- erally sufficient—But must vary according to circumstan- ces—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 con- sidered—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 prin- ciple in our rules. . . . 17?