gum; those which furnish it with most facility are sugar of milk and dextrine. The acidity of stomach which is produced in some dyspeptics by saccharine substances arises from the development of lactic acid. Milk also is apt to disagree with such individuals, not only in consequence of the difficult digestibility of its fatty constituent (the butter), but also on account of the conversion of its sugar into lactic acid. Both bread and beer contain dextrine, and are the occasional sources of this acid. The tendency which some farinaceous substances, as oatmeal and potato-starch, have to cause acidity of stomach is owing, probably, to the formation first of dextrine, and afterwards of lactic acid." (p. 526-7.)

The production of this acid requires an azotized ferment, which is either contained in the food or derived from the stomach. Tea, coffee and acid juices sweetened with sugar, sweet wines and beer, are thus liable to become acid. Sometimes the process goes on to the viscous or mucilaginous fermentation, and during these changes carbonic acid and other gases are evolved.

4. The tendency to putrescency is another quality in food which affects the changes that may occur during digestion. The gastric juice counteracts this tendency, and when putrescent transpositions have actually set in, they are arrested and superseded by the action of this fluid. When the digestive powers are feeble, probably when the gastric juice is scanty in quantity or weak in quality, this tendency in organic matters may take its origin or proceed in the living stomach. It is necessary then to consider the liability of foods to putrescency. Animal substances are more prone to this change than vegetables; pork, as remarked by Dr. Davidson, is very apt to produce nausea and putrid eructations. Some of the ill effects of putrid matter received into the alimentary canal have been alluded to under the head of water, which, when it abounds in decomposing matters, so remarkably interferes with the digestive operations. We may state, in fine, that the usual chemical metamorphoses of organic matter are more liable to occur in certain states of the system, or of the digestive organs, than in others, and that they are superseded by the solutions or series of changes which constitute vigorous digestion in the healthy subject.

5. Cookery, and the modes by which food is preserved, here become subjects of medical and scientific interest. Numerous methods have been resorted to by mankind to preserve food; as, drying in the sun, or by artificial heat, smoking, salting, pickling, preserving with sugar, or with ice, or by the exclusion of the air. Although vegetables, as olives, mushrooms, and cabbages, are sometimes salted, animal food is the chief aliment submitted to this process. It appears to be essential that it should be done before putrefaction sets in, but the rationale of the process is by no means, even now, understood. Dr. Davidson states:

"That the animal fibre is hardened and condensed by the process of salting; and that it is impossible by the ordinary methods of maceration, and subsequent boiling, to remove the salt. These facts will readily account for the more difficult digestibility of salted meat. The fibres will thus be less easily masticated and dissolved in the stomach; and the extra quantity of salt being liable to excite thirst, a tendency to overcharge the stomach with liquids will frequently be induced. Salted meat and fish ought therefore to be taken in small quantities by those who have delicate digestive organs. Meat or fish, however, which has been slightly salted, only for a few days, is frequently rendered more tender and digestible by this short process. When kept for many months in salt, it often becomes tainted, is liable to prove unwholesome, or to produce scurvy if used without a sufficient quantity of vegetable food." (p. 91.)

It does not appear that any portion of nutriment is lost; Mr. Donovan having proved by experiment, that the juices usually expelled from meat during the process of salting are mere water tinged with blood; on the contrary, salting frees meat from that which would promote putrefaction. Dr. Pereira leans to the opinion that the preservative power depends, as in the case of some metallic salts, upon a chemical combination formed with the organic tissues. However his may be, hams, tongues, and salted and smoked flesh and fish, are less digestible than fresh food, in consequence of hardness and indissolubleness of texture. The process that hardens and preserves them from putrefaction, before they are taken into the stomach, keeps them from solution afterwards. Pyroligneous acid, containing a small portion of empyreumatic oil, is best adapted for pickling fish and other animal substances. According to Mr. Ramsay, quoted by Dr. Davidson, it is sufficient simply to dip herrings in the acid of 1012 density; and beef may be kept for six or seven months, without taint, by immersion in it for one minute. Another mode of preserving food is that by inclosure in tin cases from which the air has been exhausted, adverted to by Dr. Truman, who states that Sir John Ross and his companions "dined in the Arctic regions on Christmas day, 1831, on a round of beef, some veal and vegetables, all in perfect condition; which had been left with other stores belonging to the Fury,' in those high latitudes in 1823;" having been preserved by this method; and that other portions of food brought back to England in 1835, eleven years after it was prepared, remained perfectly good. But we may here remark, that although quite fresh as to taste, they have not the flavour or sapidity of really fresh meat. Preserved milk is extremely disagreeable, and in doses of a few ounces might serve as an emetic. Berzelius is quoted, to the effect, that sugar is more frequently employed than formerly for the preservation of meat, owing to a much smaller quantity than of salt being required to prevent putrefaction. Fish when gutted may be well preserved by spreading powdered sugar inside them. Many of the preservative processes, although unquestionably chemical, are not yet satisfactorily explained.

Dr. Pereira thinks the efficacy of sugar, in the preservation of fruits and some other vegetables, is not attributable to its preventing fermentation only, but that "it promotes the solidification of vegetable jelly.” The two-fold object of cookery is to please the palate and to increase the digestibility of food. Taste being intended, with other purposes, to assist in the selection of proper nutriment, when the diet has been habitually simple and the sense continues unalloyed, it is well calculated to insure that object; "for a good taste is the truest mark of good meat and drink, and all meat by how much more savoury it is, by so much the better it nourisheth," saith Roger Bacon. By luxury and abuse this sense is both. refined and perverted. The natural desires and aversions belonging to it are to be observed only, for the most part, in infancy and very early childhood. The proper criterion of the qualities of food is afterwards little to be depended upon; we employ the most unwholesome and injurious materials; custom is law, the most acrid and nauseous substances become agreeable, and cookery, from a very simple, is rendered a very complicated art.

Whatever the estimation in which this art is held by the profession, the public, according to Dr. Truman, have appreciated its merits :

"The Romans paid great sums for cooks, who were slaves; and, if they became much celebrated in their vocation, always fetched a high price in the market. In modern times the professors of cookery are liberally rewarded for their services. The principal cook at one of the most celebrated club houses in London, is stated at one time to have had a salary of fifteen hundred pounds per annum—a much larger stipend than is enjoyed by any professor at either of the universities, and far exceeding the value of the greater number of church livings." (pp. 106-7.)

The gratification of a perverted taste, rather than the promotion of health, has ever been the primary inducement for this species of prodigality; and although our modern system of cookery may, upon the whole, excel that of the Romans in simplicity, Apician refinements have still

their devotees.

Many of the mechanical and chemical changes effected by cookery are well explained in different parts of Dr. Pereira's volume. A diminution of the cohesive force, and a complete destruction of the organization of the compound aliments seems to be a principal object. The ordinary chemical transformations, by which organic matter passes progressively into the more simple combinations of inorganic nature, are arrested. But the more essential alimentary principles, as protein, oil, and probably gelatin, ought by no means to be changed. The facts of chemistry, as they at present stand, would seem to indicate that any process, having for its result a decomposition of these principles, renders alimentary substances not only indigestible but unwholesome, and destroys their nutritive powers. The processes themselves vary extremely in their effects.

A. Roasting, after drying in the sun, is probably the most primitive mode of dressing food, as it requires but little apparatus. Being effected at a very high temperature, a great deal of fat is drained away, and water evaporates; it is necessary to guard against the chemical changes which take place in the fibrin, oil, &c., when meat is overdone; and the juice of underdone meat is almost entirely aqueous. Well-done meat contains less both of water and fat, and is most digestible.

B. Boiling. This mode of cookery is considered upon the whole as best calculated to increase the digestibility of food. From vegetables it dissipates the volatile oils, as in the onion, and also gaseous fluids. The grains of fecula in amylaceous substances are broken or split up, the heat and digestive power of the human stomach being insufficient for this purpose. Boiling also coagulates the vegetable albuminous fluids. Gummy and saccharine principles are dissolved, and sometimes injurious principles are extracted; as, for instance, any portion of solanina that may be contained in the potato. In boiling this vegetable, the liquor in the cells and intercellular spaces is coagulated, the starch grains absorb water, swell up, and distend the cells, the albumen forms irregular fibres between the starch grains, and probably also covers them with a thin film, and the cells in which the starch grains are contained separate from each other. In mealy potatoes these changes are complete, in those that are waxy they are only partially effected, hence the latter are less digestible than the former. Analogous changes are effected by cookery in apples and similar vegetables. In boiling animal food, gelatin is dissolved, and part of the nervous fatty matter dissipated; the fatty matters melt, and except when inclosed in close cells, escape; liquid albumen is solidified, as in the egg; and flesh is rendered firmer. Unknown reactions take place during ebullition, and the decoctions, or broths and soups, contain creatine, osmazome, &c., but the essential nutritive prin

ciples, fibrin, albumen, some gelatin, fat, and nervous matter remain. Mischief may be done by boiling if injudiciously managed. Albumen if boiled hard is less readily acted upon by the gastric juice and its digestibility is impaired. By prolonged ebullition at 220° Fahrenheit, as in Papin's digester, gelatin evolves ammonia, becomes syrupy, loses its property of forming a jelly, and very speedily undergoes putrefaction. Its nutritive properties are thus deteriorated if not destroyed, and it is rendered less digestible.

c. Stewing is in some respects a good method of preparing animal food, the whole of the nutritious matter of the meat being preserved, and its texture softened, but it is required to be done carefully. Soups, hashes, and even stews, if ill prepared, on account of the above-mentioned changes in the gelatin, and of the fat which they contain, are liable to become obnoxious to the digestive organs. It is proved also by Dr. Beaumont, that strong broths and soups, regarded as solutions of gelatin, and incapable of coagulation, have their digestion retarded, until, by the absorption of their watery parts, they acquire a more solid consistence.

D. Broiling is analogous to roasting, but effected more rapidly; the outside is liable to be charred, and the fat to be acted upon by the heat. E. Baking differs from roasting, as retaining a larger proportion of the oleaginous principle, also modified by heat; hence baked meat is more liable to disturb the digestive processes.

F. Frying is of all methods the most objectionable, the fat in which the substance is placed requires a very high temperature to boil; this, and exposure to the open air, renders it rancid, and promotes the various chemical changes which we have before adverted to; the albumen, as of eggs in batter, is hardened, and the food rendered less easily miscible with the contents of the stomach, for which reasons omelets, pancakes, fritters, &c., are liable to prove indigestible. In fine, any operation in which fat is subjected to a high temperature becomes objectionable, especially where the digestion is weak. This abstract will amply illustrate the scientific relation of cookery to practical medicine, and fully proves, that the more simple processes only are essential. Good cookery in these points of view is conducive to health, and no doubt also to longevity.

These being the principal circumstances, which influence food as respects its digestibility, a remark or two is called for before we enter upon the matter of the second section of the present chapter. That hunger and thirst are not affections of the stomach alone, but belong to the whole system, is true, although many deny and others doubt it. Different states of the system are manifested by these sensations, and by the digestive powers, which in health, for the most part, correspond with the natural appetite. This we apprehend is what Dr. Pereira means by the digestibility of foods being affected by circumstances relating to the organism. We can but regard this as a deviation from the usual logical precision of the writer. Idiosyncrasies may affect the digestion of the most digestible foods, as in the case of the individual alluded to at page 246, in whom mutton acted as a poison. Yet the mutton is not indigestible. However, these states of the system legitimately belong to the inquiry respecting diet, and here we are led to what we believe to be one of the most important results of the discoveries recently made in organic chemistry. Hitherto practitioners in selecting, preparing, and portioning

food have for the most part aimed simply at the adaptation of its qualities to the processes of primary assimilation or digestion. The views promulgated by Prout, and more particularly those of Liebig and his school, have rendered more obvious this additional special object in all our dietetical rules, the adaptation of food to the wants and exigencies of the whole system, or to particular structures, in secondary digestion or assimilation; or for the production of animal heat. Dr. Combe inculcates this adaptation as a principle of practice, but does not enter upon the chemical considerations. By defining more precisely the nature of assimilation, and the materials employed in the nutrition of tissues; and by determining the order and amount of their waste under the various circumstances of life, by means of an examination of the secretions and excretions; we may ascertain what alimentary principles are necessary to be supplied, and are also enabled to form some notion of the quantities required. It is not to be said that many very important results, applicable in the manner we have indicated, have yet been obtained. Still, we are assured that any system of diet which does not include a certain quantity of protein for instance, is inconsistent with that vigour of constitution by which man is enabled to labour in his various vocations; and a diet entirely divested of that principle, if continued for any length of time, is incompatible with the continuance of life. So also, by feeding animals with food having an abundance of the oleaginous principle, or of those materials which are easily converted into oil in the economy, keeping them at the same time in a high temperature and preventing exercise, we can promote the deposition of fat. These instances give countenance to the notion, that by continuing our investigations in this direction, we shall ultimately arrive at practical rules, by which nutrition may in a great degree be regulated, and by which questions respecting diet may be determined, appertaining both to hygiene and therapeutics.

II. OF THE NUTRITIVE QUALITIES OF FOOD. This subject having been fully considered in various parts of the volume, is only summarily treated of in this place. We have seen that aliments differ from each other enormously in the proportions of water to dry matter which they contain, and their nutritive powers must differ in a corresponding degree. The digestible part of the dry matter must be distinguished from that which is indigestible, as from lignin and chlorophyle. The dry material is divisible again into nitrogenized and non-nitrogenized principles:

"For whether the views of Liebig as to the exclusively nutritive quality of nitrogenized foods be or be not correct, it cannot be doubted that the mode of nutrition of substances which are devoid of nitrogen must be different from that of bodies which contain it, and whose ultimate composition is identical with that of the living tissues." (Pereira, p. 453.)

The nutritive value of the nitrogenized part is said to depend upon the relative quantities of the compounds of protein, of gelatin, and other substances containing azote; and the efficiency and utility of the non-nitrogenized part in the production of animal heat, to depend upon the quantity of carbon and hydrogen, and the modes in which these elements are combined. These views, if correct, must originate an entirely new feature in practice. In prescribing dietetical rules, the whole amount of the various alimentary principles, and of the elements of food, that any particular diet may contain, respecting which an opinion has to be offered, must be considered. Looking to the general tendency of these doctrines,