aliments between their real nutritive qualities and those which, à priori, they might be expected to possess, from a consideration of the elements and principles which they contain. This is seen in the leguminous seeds, which contain more nitrogen and more of the proteinized principles than the cereal grains; yet for man they are less nutritive. Liebig attempts to explain the fact upon the principle that they are deficient in earthy phosphates, but numerous considerations lead to the inference that this cannot be the only cause. We are inclined to believe that in the case of man, a too-highly concentrated state of the proteinized compounds in his food, apart from the consideration of the absolute quantity which this may contain, is less consistent with perfect nutrition and continued good health, than when these same principles are more completely divided, and diluted with others reputed to be less nutritious; as starch and gum, and in some cases oil. So that, although no doubt the commercial value of wheat, for instance, may be measured by the quantity of gluten entering into its composition, it by no means follows that if employed alone as food, its nutritive value could be measured by the same standard, or that flour, which contains a very large quantity of gluten, is, upon the whole, better adapted for human food than that which contains a fair, moderate

average.

If the nutrition of our bodies depends upon certain principles being received into the system, as component parts of our daily diet, how important is it that we should be in possession of correct analyses of every substance employed as food. Questions relating to the diet of individuals or of communities must be referred for solution to these analyses ; and in many instances it is upon their accuracy only that any just conclusions can be founded. Bearing in mind that the subject of diet is intimately involved in those of air, exercise, and other hygienic influences, but for the present limiting ourselves to such considerations as belong to the former, the great question to be solved will be-What quantity of the different alimentary principles does any particular system of diet embrace? It is only by the knowledge we have already obtained of these principles, and by reference to these analyses, that we can at all comprehend the results of the habits of the Irish peasantry, of whom it is said there are hundreds who never tasted bread, and millions who live chiefly on potatoes. The potatoes are for the most part accompanied with butter-milk for drink, and frequently with salt herring; hence we have all the staminal principles of Dr. Prout, and all that is essential of the alimentary principles of Dr. Pereira-casein, oil, starch, sugar, salts, and water; the question reducing itself to whether the food as a whole contains a sufficient quantity of these materials. A labouring Irishman will consume from seven pounds to ten pounds per diem of potatoes. If we examine this question in relation to the nitrogenized principles, then ten pounds of potatoes are equivalent to nearly one pound and a half of good wheaten bread, and this, with the protein of the butter-milk, herring, &c., may be regarded as sufficient to supply the wants of the system, and to support "the finest and hardiest race of peasantry in the world." From seven to ten pounds of potatoes contain from fourteen to twenty ounces of carbon, an abundant quantity for the maintenance of animal heat. To the remark, that numerous individuals among the Irish are unable to obtain so large a quantity of food as here indicated, and that this quantity

is below the standard of the English labourer, as measured by the quantity of proteinized principles, may be added, that the strength of the Irish is very apt to fail them at a comparatively early age; that the vital force of an indifferently fed Irish labourer is below that of a well fed English labourer; and that experience has shown the former to be particularly obnoxious to diseases of debility. Rice again is said to be "the grand material of food on which a hundred millions of the inhabitants of the earth subsist;" but we well know that these people live not on rice alone; milk forms a common constituent of their food; and independently of this, in proportion as they depend on rice for nourishment, do they consume the greater quantity. In Alexandria, the food of the peasantry, as the Fallaheen women, is chiefly a few lentils, rice, dates, bread made of beans or oatmeal paste, perhaps a little sour Arab cheese, with salt, sometimes black olives, a small quantity of honey, or some gourd or water-melon. These contain all the essential principles of nourishment; but the people get little of them, consequently they are a sickly and emaciated race, and death from absolute starvation is no uncommon thing. Every problem of this kind to be solved must be worked upon chemical data, and our knowledge must turn upon dietetical statistics on a large scale; without which there can be no hope of discovering comprehensive principles. A question again suggests itself here, which does not appear at present to have been much entertained by physiologists: What quantity of each of the elements or of the staminal principles is necessary for continued health in the various states and circumstances of human existence? This question has been most inquired into in reference to the element carbon; but our information is not yet very precise. Dr. Pereira leans to the opinion (p. 10) that about one pound is required daily, by a hearty adult; subject to considerable variations, according to age, sex, peculiarities of constitution, temperature and density of air, occupation, clothing, &c. Both carbon and hydrogen being regarded as fuel for the production of heat, besides the causes of variation mentioned, the quantity demanded of the former, must depend partly upon the quantity of the latter, available in the economy. This has the greater influence, in so far as that a given quantity of hydrogen, as compared with the same quantity of carbon, combines with double the amount of oxygen, and the heat developed is proportionate to the oxygen employed in these processes of combustion. Again; of the nutritive principles: if it be a fact that some materials in the food, although incapable of affording nourishment of themselves, yet contribute essentially to nutrition when taken in conjunction with others, the question as to quantity can be answered, in the present state of science, only approximately.

II. OF DIET.

This brings us to the consideration of "the adaptation of aliment to the different wants and conditions of human existence," constituting the second part of Dr. Pereira's volume; comprised in five chapters: 1. Of the Digestibility of Food. 11. Of the Nutritive qualities of Food. III. Of the times of Eating. IV. Dietaries. v. Of Dietetical regimen suited to disordered states of the Digestive Organs. We shall deviate in some measure in our notice of these subjects from the author's order of arrangement.

I. OF THE DIGESTIBILITY OF FOOD. The notion insisted upon so much by Fordyce, and in fact entertained by his predecessors, that all food must. be digested before it can afford any nourishment, has by no means been set aside by any recent discoveries in organic chemistry. All food must undergo certain special changes in the prima viæ before it can constitute chyle, and in all animals it remains there, for a certain length of time, for the purpose. This proposition is true of milk, of the albumen of egg, of the staminal principles of Prout, of the alimentary principles of Pereira —even of oil, which appears to undergo a slighter modification than any other substance, previous to its entrance into the lacteal vessels. The comparative digestibility of the innumerable varieties of food, and of their constituent parts, is of the highest practical importance. As remarked by Cullen, "the powers of the stomach being given, there is a difference in the digestibility of different substances, arising entirely from their dif ferences of (composition and) texture." All writers have made this difference a principal subject of investigation, but their decisions have been too frequently founded upon imaginary qualities and false analogies, and the sciences either of chemistry or physiology do not even now supply many certain or very extensively applicable data. Dr. Pereira considers in this chapter, which is very short, the digestibility of food as "affected by circumstances relating to the foods themselves," and as "affected by circumstances relating to the individual or organism." In so far as these are separable, we shall confine ourselves, under the present head, to an illustration of the former, which we hold to be the more correct application of the term "digestibility."

1. The cohesive force is obviously opposed to digestibility, and tenderness of fibre promotes it; hence nature has provided the means of securing minuteness of division by appropriate masticatory organs, and many influences to which food is subject also promotes digestibility by lessening this force. The incipient decomposition of animal food, and violent muscular exertion used by animals immediately before death, act in this way. The admixture of a due proportion of water with substances intended for digestion is most necessary; and nature in this instance again has secured the direct fulfilment of her own objects by providing organs for the secretion of saliva; for, whatever further purposes saliva may serve, this is unquestionably one; and the comparative facility of digestion of various substances frequently turns upon the degree of readiness with which they become incorporated with it. Dr. Beaumont found that tendon, owing probably to its compactness of texture, required five hours and a half for complete digestion in the stomach, whereas, jelly required only one hour.

2. Chemical constituents. Some of the alimentary principles are naturally slower and more difficult of digestion than others. The gelatinous principle in many of its forms is by no means easily acted upon in the stomach. It has to be remembered that from ten to fifteen grains of dry gelatin renders four ounces of fluid a tremulous jelly; that substances taken into the stomach require a certain degree of pulpiness to enable them to be acted upon by the stomach, for which purpose their more fluid parts are absorbed, and that semi-fluid substances, as jelly, are for the most part swallowed without insalivation. Hence soups containing much gelatin, the juices of fruits composed of the pectinaceous principle,

and even mucilaginous fluids, are apt to remain in the stomach for some time before the absorption of their fluid parts takes place. The oleaginous, as compared with most other alimentary principles, has been understood by all writers to be slow and difficult of digestion. This is shown by the natural antipathy which the tender stomach of the young has to uncombined fat, by oily matter frequently becoming uneasy in the stomach, and by its effect on valetudinarians. "Two members of my family," says Mr. Thackrah," were annoyed with disorder of the stomach after breakfast. One in particular was uneasy, depressed, and irritable, during most of the forenoon. Plain bread or toast was substituted for buttered toast, and the disorder was removed in the one case and materially relieved in the other." Dr. Pereira insists much upon this point. Óleaginous matters, he states, are first converted into liquid oil in the stomach, then they form a kind of emulsion containing myriads of oily globules, in which form they are absorbed by the lacteals. This process, and perhaps some other unknown change, is affected by the bile, which is found in the stomach during the chymification of fatty substances.

"The popular notion that oily or fatty foods' cause bile' in the stomach, is not, therefore, so groundless as medical men have generally supposed. From Dr. Beaumont's observations and experiments, it appears that oil is slowly, and with great difficulty, acted on by the gastric juice; but that the admixture of bile greatly accelerates chymification. Perhaps the alkaline property of the bile partly contributes to this effect." (p. 171.)

Fat is also liable to float on the surface of the stomach as an oily pellicle, becoming odorous, sometimes highly rancid, and exciting heartburn, nausea, and eructation, or at times actual vomiting; and the greater tendency of some varieties than others to produce these effects, depends upon a greater facility in evolving volatile, acrid, and irritating acid and non-acid principles. Mutton fat contains hircic acid, and butter no less than three volatile acids-butyric, capric, and caproic acids; and it is by the changes of composition effected by heat, that oily and fatty substances, after cookery, are more apt to disturb the digestion than fresh and sweet new oil as employed in salads. The observation made by Dr. Combe and others, that the fat of salt pork and bacon is less apt to prove injurious than fresh animal fats, is referred by the author to some change effected in the process of curing. Upon these principles, Dr. Pereira explains the liability of numerous aliments, containing a large proportion of oil, to disturb the stomach. The yelk of eggs, the liver and brain of animals, milk, rich cheese, fried dishes, puddings, cakes, chocolate, the oily seeds, as the almond and walnut, hashes, stews, and many foods in which the oily principle is liable to be taken "in a concealed form," for instance: the indigestibility of the salmon, eel, sprat, and herring, as compared with the whiting and haddock, is owing also to a greater proportion of oil in their composition.

Of the compound aliments, vegetables are held to be slower of digestion than animal foods, and crude vegetables to be more difficult to digest than meat or farinaceous substances; but a discrepancy of opinion exists on the subject. Dr. Cullen gave as a reason, that he had known portions of apple eructated without alteration two days after they had been swallowed, which undoubtedly happens; but Dr. Beaumont found that apples are easily digested in the stomach, requiring only about an

hour and a half for the purpose. Imperfect mastication and insalivation accounts for the fact cited, and the structure of the teeth in man and herbivorous animals compared, indicates that vegetable foods require these processes more particularly. It may be here stated, that experiments made on animals by Schultz, led him to the conclusion, that crude vegetables and other indigestible matters are apt to excite a rapid motion of the stomach, by which they are propelled through the pylorus unaltered, in consequence of which they disturb the after stages of the digestive process. The evidence adduced of late, favours the conclusion, that vegetables are for the most part easily digested in the healthy human stomach, and that the argument founded upon experience is in this, as in many other instances, fallacious; the disturbances excited by their use depending rather upon other causes than any inherent quality which prevents or retards their digestion. To this remark, however, there are some exceptions.

3. Proneness to acidity is regarded by Dr. Pereira, with all the writers on diet, as a quality which contributes to render various kinds of food indigestible. Hippocrates and Galen, observing that the use of acescent vegetable matters augments the natural acidity of the animal humours, referred many evils to a superabundance of acid; and Sylvius and the chemists attributed half our diseases to an acid acrimony in the system. Very vague notions are even now entertained on this subject. We have, in the first place, to distinguish between the effects of acids taken into the stomach ready formed, as part of the food; and secondly, the effects of acids developed in the stomach from the food. Reasons are given, in the first part of the work, to show that an acidulous alimentary principle is not only digestible and wholesome, but also necessary. Combining with bases in the alimentary canal, the vegetable acids convey saline compounds into the blood, which have their ulterior uses. To acetic acid, in particular, the indigestible qualities of various fruits and other substances have been attributed, yet this acid is a component part of the gastric juice, and one of the best solvents of proteinized substances. Used in moderate quantities in the healthy stomach it promotes digestion. Many substances containing ready formed acids are liable, from other causes, to disturb the digestive organs and produce pain, diarrhoea, and colic. Fruits imperfectly masticated and insalivated, received into the stomach with seeds, flakes of integument, &c., must excite the muscular action of that organ, and their own propulsion into the duodenum, before the necessary changes have been effected. Vegetable matters thus hurried into the small intestines, acting as foreign bodies, are well calculated to create the disturbances just mentioned, which have been too exclusively referred to their acidity. Escaping the chymous changes, they are not prepared for the duodenal changes. The development of gases, increased secretion from the alimentary tunics, and spasms, are the well-known

consequences.

But some foods undergo fermentation in the alimentary canal, an important circumstance connected with proneness to acidity. The acetous fermentation has for a long time been recognized, but the lactic acid and viscous fermentations are also known to occur. Dr. Pereira states: "Lactic acid is one of the substances derived, in part at least, from the food. The alimentary principles which yield it are sugar, dextrine (starch-gum), and

XXXIII-XVII.

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