DR. COMBE ON DIGESTION AND DIETETICS.
D. COMBE must be placed in the first rank of the popular ex- pounders of science. He may want the sprightly elegance with whieh some few writers have been able to animate dry or difficult subjeets,—ahhough their airiness often degenerates into levity : several authors may have equalled him in the clearness requisite to explain abstruse or complex principles; but he seems to us to stand alone in the power which he possesses of imparting interest to the matters that employ his pen, without deviating from the sobriety Will gravity proper to philosophic exposition. For some of the attention he excites in the mind of the reader, Dr. COMBE its unquestionably indebted to his subjects ; which, addressing the corporeal tbelings and sympathies of' every one, come more directly home to the bosoms of the generality than even the most attractive kind of fictions. As experience, however, shows that popular medical treatises may be written, and well written, without approaching the effect produced by Dr. Comm:, it is worth while to anal) ze the combination of' qualities which gives to his writings their peculiar character. And the first of these, it is almost needless to say, is a perfect mastery of his subject, by which he is able to reject every thing not essential to its full expo- sition. The next is the distinct and lucid manner in which the essentials are presented to the mind. To excite and sustaiu attention, more than these, however, are necessary ; and in the case of Dr. COMM, they will be found to consist in the skill with which he selects the most striking facts connected with his subject to illustrate or enforce its principles—the directness with which every thing is made to bear upon that practical matter our own wellbeing—the reflecting penetration that enables the author to deduce new truths from well-known facts, which others have passed over without perceiving their relations, and the faculty he possesses of putting old things in a new light. In addition to all this, Dr. COMBE possesses great ease and clearness of style; its very- diffuseness being in one sense a merit, because of the novel and abstruse nature of some of the subjects the author has to expound. It is acutely observed by COLEEiTIGE, that a senten- tious style is a defect if it requires more time and pains to under- stand it than would have been necessary with a Biller diction.
The volume which has occasioned and which illustrates these remarks, is intended as a companion to the author's Principles of Physiology applied to the Preservation (If Health. It may be remembered, that one distinct feature of that work was an account of some of the excretions by which superfluous and effete matter was thrown off the system. The object of the present is to describe the operations by which the foreign substances taken into it are prepared fimr becoming bone of its burn: and flesh of its flesh, as well as to derive from this description some practical rules for the attainment of that grand essential to happiness a good stomach. With this view, the book is divided into two parts; the first em- bracing the physiology of digestion, the second containing the general principles of dietetics deducible front the natural laws of digestion. Of these two divisions, the first is the most satis- factory and interesting, from the nature of its subject ani the popular novelty of much of the information it imparts, or the force and freshness with which obvious truths are presented. We have most of us, for instance, heard that some loss of matter, even in inanimate substances, is consequent upon action however trifling the action may be : but how clearly is the principle impressed upon the mind by instancing " 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!" The loss of substance which living things undergo, and the power they possess of replacing this loss by continual fresh supplies, is familiar to all : but how few have thought upon the wise provision of appetite !—for, universal as is now the practice of eating and drinking, it would never have done to have made those actions a matter of duty. " If man," says Dr. COMBE, "hail no motive more imperative than reason to oblige him to take food, he would be constantly liable, from indolence and thstightlessness, or the pressure of other occupations, to incur the penalty of starva- tion without previously being aware of his danger." To prevent this is the task of hunger and thirst: and, before expounding the principles of nutrition which necessarily spring from them, Dr. COMBS investigates their nature at considerable length ; attributing their origin to the waste which the body has undergone, and showing that their seat, though supposed to be the stomach, is in reality the brain. He next, in a chapter °' remarkable clearness, explains the character of the teeth both. in man and other animals, as well as the uses of mastication, saliva, and deglutition. The act of swallowing naturally leads him to the stomach, where all that we swallow is subjected to its first transmutation; being converted into a uniform substance called rhyme, by the power of the gastric juice, aided by heat, motion, and a flow of blood to the stomach. And this section of the book is enriched, not only by the soundest views and most striking, facts already known to the medical world, but by the extraordinary experiment:, the American physician Dr. BEAU- MONT was enabled to make on a Canadian named ST. MARTIN. This person—luckily for science—had a portion of a couple of bis ribs carried away by a gun-shot wound, and a peep-hole made into his stomach, which remains even till this day ' • Nature, failing in her attempts to make him wl ole, baying doubled up the (mat of the stotnach and formed a valvt removable at pleasure. Of this interesting circumstance Dr. lisaemoNr took advantage ; engaging Sas MARTIN, at considerable expense, to live with him, and submit to innumerable experiments, the pith of which is embodied in two chapters of Dr. Comns's book. There the curious mov read how the votary of science inserted an indigestible sub- stance into the orifice, and decided that the gastric juice was secreted by contact alone, although its secretion ceased as soon as it ascertained its incapability of acting on the strange visiter. Ile will there ascertain the different foods on which Dr. BEAU- MONT fed ST. MARTIN, and the various stales in which he found theta at various times as he peeped through the loophole into Nature's laboratory. He will learn how the muscular action of the stomaeh keeps substances within it in constant motion towards the entrance to the bowels, (whenee, if not reduced to chyme, they are rejected and return,)—as the indefatigable experimenter dis- covered when he inserted his thermometer, which was gradually drawn downwards ; one use of this constant movement being to remove the chyme from the exterior of the food, and enable the gastric juice to continue its action on the yet undigested parts. Ile will learn, too, the experiments made on various eatables with pure gastric juice in phials kept at different temperatures,—proving that beet is necessary to digestion; or with gastric juice and half- digested filed extracted from the stomach,—showing that this juice alone is sufficient to digest, though not so quickly; or minced meat put into the stomach without swallowing, and the digestive operations which followed its insertion,—whence Dr. BEAUMONT infers that saliva is not a very essential element in digestion ; besides a variety of other experiments both curious and useful. But to return. When the nod has been reduced to chyme in the stomach, it passes into the bowels, where it meets the bile from the liver and the pancreatic juice from the pancreas,—a junction from which chyle is produced. On the internal surface of the bowels an immense number of minute vessels are ramified, which absorb or suck up, sponge-fashion, the chyle after it is formed. These lacteal vessels gradually coalesce into larger trunks ; which, after passing through the mesenteric glands, terminate in the thoracic duct, by which the chyle is conveyed into the vein that brings back the venous blood to the lungs. There, as was shown in Dr. COMRE'S Principles nf Physiology, it is, by contact with the atmospheric air, converted into arterial blood, and is fitted to supply the place of the old particles sensibly or insensibly thrown off from the system. When this supply of chyle fails, the system, by appetite, gives signs of its wants: if they be not attended to, faintness ensues, then wasting, and at last death. If materials for more than this just supply is given, the stomach is over-tasked ; the food, after fre- quent rejections, is passed into the bowels undigested ; general uneasiness follows; and if the plan of over-eating be persisted in, dyspepsia with its train of evils is induced; or, where the stomach is capable of bearing such over-tasking, the patient becomes plethoric, and liable to be carried oft by apoplexy or the first attack of an acute disease.
The section on chylification, absorption, and the mysterious processes which complete the function of nutrition, is equally clear and instructive with that on chvanification ; and the results de- scribed are equally wonderful. But, as the organs concerned in these processes lie deeper than the stomach, and are not so easily seen or reached, experiments either by iirspection or vivisection of animals are proportionally difficult or impossible. Practically, however, this is of small consequence, as whatever conduces to chymification seems equally conducive to chylification or intesti- nal digestion.
Having thus finished Nutrition, Dr. COMM; proceeds to the second part ; which, as we have said already, is less effective,— not, however, from any falling-off in the author, but from the sheer necessities of his subject. The exposition of Digestion is specific and complete ; the rules we must follow to procure a good one are general, and appear somewhat vague. Nor was it possible that they should be otherwise. The use of the stomach and bowels is to repair the waste of the system ; and the supplies should be proportionate to the expenditure. Yet who can lay down one or several rules of diet that shall be applicable to individual cases ? The growing youth requires more than the mature man ; the active than the sedentary; the healthy than the invalid. Much, too, depends on the state of mind, and the potent influence of the nervous system. The prosperous person, who sits down to table with a cheerful soul, disposed to please and be pleased even with trifles, will bear more, and extract more nourishment from it, than the harassed, anxious, or thoughtful man, whose mind is revolving matters of a distressing or exhausting nature. The diet adapted for a bilious temperament would be unfitted for the sanguine, the nervous, or the lymphatic, and vice versa. Ab- atractedly, noon is the best hour for dining; and the farmer, who leads a natural life, rising early and passing his time actively in the open air, generally dines about mid-day. The man of fashion, who gets up after the ether has dined, prudently defers his prin- cipal repast till eight or nine o'clock at night, and perhaps takes a supper at two or three in the morning: not that these hours are good in themselves, but they are well enough fitted to the life he leads. A similar uncertainty prevails with regard to the intervals between meals, though the extreme points are much more limited: the strong and active will be ready far a fresh supply in four and a half or five hours ; the weakly and sedentary may go as long as six ; or these periods may be extended if a slight intermediate repast be taken to preveet thintness. In short, whilst disease is. absent, the stomach is a very accommodating organ, provided it be managed mid the only rule that we can glean of universal application is that which MILTON puts into the mouth of Michael- " The ink of not too much."
Of course, irat we have said is to be considered as mere indicia of the leading points of the solume,—a skeleton, withuut flesh, blood, feature, or roundness. Nor u ill any specimens that we could offer convey any idea of the work, unless we could extract an entire section. We will, however, take two or three short pas- sages, as samples of the author's manner.
II UNCER .5 ND 'nil RST.
The sensation id' hunger is commonly referred to the stomach, and that of thirst to the tipper part of the throat mol back of the mouth,—and correctly enough to this extent, that a certain condition of the stomach and throat tends to produce them. I tttt, in reality, the sensations themselves, like all other mental affections and emotions, have their seat in the brain ; to which a sense Of I he V011016011 Of the stomach is conveyed through the medium of the nerves. In this respect, appetite resembles the senses of seeing, hearing, and feeling; and no greater difficulty attends the explanation of the one than of the others. Thus, the Callse whirl, excites the sensation of colour, is certain rays of light striking upon the nerve of the eye; and the cause which excites the perception of sound, is the atmospherical vibrations striking upon the nerve of the ear : but the sensations themselves take place in the brain, to which, as the organ of the mind, the respective impressions are conveyed. lo like manner, the cause which excites appetite is an impression made on the nerves of the stomach ; hut the feeling itself is expo ienced in the brain, to which that impression is conveyed. itecordingly, just as in health no sound it ever beard except when the external vibrating atmosphere has actually impressed the ear, and no colour is perceived unless an object be presented to the eye, so is appetite never felt, except where, bum want of food, the stomach is in that state which forms the
proper stimulus to its nerves, and where the communicatiou between it and the • • brain is left free and unobstructed.
Thirst is generally said to have its seat in the hack of the mouth and throat; but the condition of these parts is merely a local accompaniment of a want experienced by the whole frame, and perceived by the nervous system. Local applications, accordingly, go but a short way in giving relief, while the intro- duction of fluids by any other channel—by immersion in a bath, by injection into the veins, or thiough an external opening into the stomach—is sufficient to quench thirst uithout the liquid ever touching the throat. The affection of that part, therefiac, is merely a result of the state of the system, and not itself the cause of thirst.
SURPRISING POWER OF DIGESTION.
If, in the whole animal econiony, where all is admirable, there be one ope- ration which on reflection appears more wonderful than another, and which evinces in a higher degree the prodigious resources and power of the Creator in fashioning every thing to his own will, it is perhaps that by which the same kind of nutriment is extracted from the most opposite varieties of food con- sumed by living beings. For, singular as it may appear, recent researches tend to establish the fact, that, even in animals differing so widely in their aliment as the herbivorous and carnivorous quadrupeds, the ultimate products of digestion in both—the chyle and the blood—are identical in composition, in. to far at least as can be determined by their chemical analysis. Remarkable, however, as this uniformity of result undoubtedly is, it becomes still more striking when we contemplate the variety of sources from which focd is derived for the support of animal life. To use the words of an able writer already quoted, " There is no past of the organized structure of an animal or vegetable, however dense its texture or acrid its qualities, that may not, under certain circinnstancea, become the food of some species of insect, or contribute in seine mode to the support of animal life. The wore succulent parts of plants, such as the leaves or softer stems, are the principal sources of nourishment to the greater moldier of larger quadrupeds, to multitudes of insects, as well as to numerous tribes of other animals. Some plants are more particularly assigned as the appropriate nutriment of particular species, which would perish if these ceased to grow : thus the silk-worn, subsists almost exclusively upon time leaves of the mulberry-ft re ; and many species of caterpillars are attached each to a particular plant, which they prefer to all others. There arc at least fifty dif- ferent species of insects that feed upon the common nettle ; and plants of which the juices are most acrid and poisonous to the generality of animals, such as euphorbitun, henbane, and nightshade, afford a wholesome and delicious food to others." Nor are the precision and accuracy with which the same fluid, the blood, affords to ever!' structure of the body the precise species of nourish- nwnt or secns sln which its elementary composition requires, however different each may be from the rest in chemical qualities, less admirable and extraordi- nary than its own original formation from such a variety of materials. To bone the blood furnishes the elements of hone with unerring accuracy ; to muscle the same blood furnishes the elements of muscle, to nerves the ele- ments of nerve, to skin the elements of skin, and to vessels the elements of vessels ; and yet, while each of these differs somewhat in composition from the others, the constituent elemeuts of the blood by which they are furnished are everywhere the same. Similar phenomena, indeed, occur in the vegetable world; but this, instead of diminishing our wonder, rather tends to augment it. The same elements, extracted from the same soil, are converted into every variety of vegetable pro- duct, into haves of every shade of green, flowers of every form and tint, and juices of every quality, from the deadly poison up to bland and life-sup• porting milk. Nay, even in the same plant,; as in the poppy, we sometimes find the seeds and the capsule which covers them endowed with the most oppo- site properties. It would be very interesting to discover by what resources Nature thin& effects the production of the same kind of nutritive fluid or chyle from so great a variety of substances, and apportions to every part the precise elements of which it stands in need : but it is doubtful whether the human faculties were ever designed to penetrate so far into the modes of vital action ; and, in as mean time, it will be better for us so confine our attention to that branch of the inquiry which bears a direct reference to our own welfare.
The end which Dr. Comsz proposed to himself in this volume,
was not to bring forward any new discoveries, or to lay down rules for indigestion, but popularly to unfold the laws by which diges- tion was carried on. This, we conceive, he has completely achieved. Whether this knowledge only was necessary, as he seems to think, for the introduction of a more general adherence to the principles of Dietetics, may be questioned. As regards third parties, some improvement may be expected. The mother and the nurse, who have thoroughly studied the volume before us, may no longer persist in cramming the child or the invalid with food, when the stomach is not in a state, for instance, even to secrete the gastric juice. With respect to the direct effects upon eaters, we antici- pate slender results. The world will read, admire, and applaud Dr. Comas on Digestion and Dietetics, and then go on in its usual way, eating what it likes, and digesting what it can.
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