the component parts of food must be studied in reference to the wants of the system, and to their nutritive and other effects, not only by the day or week, but for more lengthened periods; and for the purpose of arriving at an opinion as to the suitableness of any given diet, we must determine the amount of carbon, hydrogen, nitrogen, protein, &c., which it contains. For this purpose accurate and well-constructed tables of the component parts of different kinds of food will prove extremely useful. Dr. Pereira's work contains several such, that at page 454 showing the average quantity of dry matter, moisture, carbon, and nitrogen, in various alimentary substances of commerce, may be particularly referred to.

III. RULES OF DIET. A matter of some consequence is this: heedless persons, and those who are unwilling to have the gratification of their appetites controlled, or restricted within reasonable limits, frequently urge that dietetical rules are useless and unnecessary. They maintain this assertion by an appeal to their own experience, bringing in support of it the cases of individuals who have lived to a very old age, of whom Parr and Jenkins are cited as examples, although erroneously, as having done so without following any particular rules of health. Such arguments are frequently employed against the advice and prescription of the medical practitioner. In support of the same assertion also, a doctrine taught by Celsus is not unfrequently mistaken even by medical men ; " modo plus justo, modo non amplius assumere." But this is itself a rule, and as Hallé and others have interpreted it, by no means a sanction to excess or carelessness of any kind. Without lending any countenance to that kind of over-solicitous attention to the health which belongs to a luxurious age, as one of its refinements, it may be fairly questioned, whether any man above a certain class of society stands the slightest chance of attaining a good old age, who does not adopt rules of diet adapted to his age, particular constitution, occupation, and habits of life. As remarked by Sir J. Sinclair, savages have their rules, which are instanced in the self-denial of the American Indians, and of the ancient Germans, with a view to preserve their strength. "Peasants, labourers, and other hardworking people are placed in that situation where few rules are necessary, because their whole lives are a series of indispensable attentions to air, to exercise, to moderation as regards diet, drink, &c. . . . Rules they do observe, and for the most part every old person will be found to have his maxim of health." Plutarch, Galen, Cornaro, the Cardinal de Salis, all of whom attained a very advanced age, had their precepts of health, which are still extant. Not only for the purpose of relief or cure when the functions of life have become deranged, and the organs diseased, but even in the absence of these, for the preservation of health, no reflecting person can doubt the efficacy of rules. The mistake has been in endeavouring to lay down one principle for all mankind, and in prescribing general rules without a sufficient regard to individual constitutions.

IV. QUANTITY OF FOOD. In the present state of our knowledge it is impossible to offer any fixed standard by which to determine the quantity of food required for any given individual. At the same time, the fact that medical and other official authorities are daily called upon to form diet-tables for large classes of their fellow-men in hospitals, prisons, workhouses, schools, and other public institutions, the importance of arriving

at the closest, possible approximation to such a standard becomes selfevident. But in pursuing this object we must be careful, as Dr. Davidson remarks, neither to lose sight of the many circumstances which modify the quantity of food required, nor to confound the quantity barely sufficient to maintain existence with that required to ensure vigorous health and longevity. Of the circumstances by which the quantity is affected, Dr. Davidson mentions two only-absolute bulk and exercise; in touching upon which, he alludes to the exceptional cases in which very slender men far excel their bulkier brethren in their daily alimentation. Liebig's principles are to be depended upon, the amount of food required for any individual ought to bear a relation-1st, to his absolute bulk; 2dly, to his expenditure of vital force, as measured by the amount and kind of bodily and mental exertion which he undergoes, and the length of sleep; 3dly, to the expenditure of caloric as influenced by climate, season, clothing, artificial heat, and evaporation at the surface of the body; 4thly, to the growth and decay of the body in infancy and decrepitude.

If

A careful consideration of the doctrines propounded by Professor Liebig in his late work, and of a vast number of facts relating to the variable habits of mankind as respects diet, and of the effects of these habits, leads to the inevitable conclusion that, especially at the period of what may be called stationary adult age, as in different species of animals, so in different individuals and varieties of the human species, there exist fundamental differences in the constitution, as to the degree of rapidity with which the molecular changes take place in the vital tissues. These differences may be hereditary, constituting an important feature in the various temperaments, or they may be acquired during the periods of growth and early nutrition; but, whatever their origin, the more or less rapid metamorphoses which they imply characterizes in part the individual constitution. Without going so far as to agree with our friend Mr. Grisenthwaite, that there is no such thing as waste and reparation in the animal body, we think that in some constitutions the quantity of matter changed daily is very small indeed. In others it is much more considerable, and the differences between different individuals in this respect is much greater than has been imagined. One man, accordingly, requires a much larger quantity of the staminal or alimentary principles of diet than another of the same weight. This is true of the living structures as a whole, and even particular structures or tissues differ from each other in the same respect, laying the foundation probably for particular idiosyncrasies and habits.

The proportionate size of the different organs has also its influence over the quantity of food which an individual consumes. Whether from original conformation or from habits of abstinence or repletion, the human stomach varies greatly in this respect. Our own observation, in repeated post-mortem examinations, has convinced us that an enormously large stomach is by no means conducive to longevity. One of the largest we have ever seen was in a woman who had been an enormous feeder, was extremely fat, and died at the age of fifty-six, suddenly,being anæmic, her muscles blanched, and having a large cholesteric calcuJus in the gall-bladder. We have observed the stomach of a very moderate capacity in old people. The absolute capacity of the stomach must have something to do with the quantity of food required, and although

the size of this organ cannot be accurately determined during life, its property of distensibility and the habits by which individuals act upon this property must be regarded in rules of diet. So also Dr. Davidson

must be correct when he says:

"If one man have larger lungs, greater extent of skin, and more muscle than another man, he of the greater capacity must consume more carbon and nitrogen in the support of these functions; and hence will require more food containing these elements. Greatly, however, as some men differ from others in natural size, this is as frequently owing to accumulation of fat; and a man may thus nearly double his weight without increasing the capacity of his lungs, the size of his muscles, or the number of his cutaneous pores. Men who have thus increased their weight by corpulency do not, for this reason, require the same amount of food as those of similar size who are favoured with no such covering; and it is possible that the fat when once formed is allowed to remain partially dormant; and hence its actual weight is supported by less food than was required for its formation." (p. 27.)

It may here be remarked, that the cases of Cornaro and of the eastern Christians who retired from the persecutions to the deserts of Egypt and Arabia, living to a great age upon a few ounces of bread and herbs with the pure element for drink, are unquestionably instructive, and should not be lost sight of. But erroneous inferences have too frequently been drawn from them, and the sources of error are in the omission to allow for the effects of climate, age, exercise, or rest, and certain habits. Probably many of these individuals lived to be 115 or 120 years of age. The facts illustrate the principles developed by modern science: they took very little exercise, were at such an advanced age that the change of matter was extremely slow, and living in warm climates as saints and hermits are wont to live, in the shade and quietude of their caves and grottos, they required very little fuel for animal combustion. The diet suited for this combination of circumstances has been ill-chosen as the prototype of that which is necessary for mankind in general. The principles of science appear to be equally well borne out by the numerous instances of longevity in various parts of England, in which the diet has always been plain, simple, and abstemious, but as required by the greater coldness. of the climate and the greater activity of its inhabitants, much more abundant than in the former cases.

These various circumstances serve to explain how it is that many individuals not only suffer no injury from a large quantity of food, but absolutely require it. How others, on the contrary, preserve health on the sparest diet. They show that one constitution demands more or less azotized or non-azotized or oleaginous food than another. By taking into consideration these modifying circumstances, many seeming discrepancies, respecting the diet employed by different people, will vanish. These circumstances determining the natural appetite ought to be taken into the account when vicious customs, or the causes of disease, or anything whatever, has occasioned the sensations no longer to be depended upon, and has given origin to the necessity for laying down some rule as to the quantity of food to be taken by an individual; and in the construction of dietaries.

The absolute and proportionate quantity of liquid necessary for the human constitution is another important consideration. Hoffman laid it down as a principle that three parts of the ingesta ought to be fluid in

proportion to one of solid; founding this upon the experiments of Boyle, who had ascertained that the blood contains three of fluid to one of solid constituent parts. Liebig makes the proportion of dry matter in the blood twenty per cent. Different writers on dietetics have taken very different views of this matter. To twenty-four ounces of solid food Cheyne allowed forty-eight ounces of fluid. Arbuthnot attached great importance to the principle of keeping the blood and other fluids in just proportion to the capacity and strength of the vessels, there being more danger from too small than from too great a quantity; but too much fluid weakens the activity of the digestive powers. Several authors have urged, we believe with propriety, the inconveniences of too little fluid, in producing costiveness, and leading to a faulty composition of the blood in the direction of a too great proportion of the red corpuscular part to the serum. The rule laid down by Hoffman is probably not far from right, but the proportion should be calculated upon the dry materials of food, not as it is commonly used. Thus dry rice when prepared for table combines with so much water that drink is hardly required with it; but bread, containing no more than forty per cent. of water, would require above its own weight, to be furnished either by the salivary glands or in the form of drink, to render it sufficiently fluid for the different stages of digestion, and for its conversion into chyle and blood. Any rule of this kind can be admitted only in a very general way, for when, from any cause, a greater quantity of fluid than of solid material is dissipated, as happens under a variety of circumstances, more fluid must be taken into the system. There are two classes of cases in which thirst is induced; those just mentioned; and where materials foreign to the blood, as poisons, or an excess of some of the healthy constituents of the blood, as of its salts, are received into that fluid. If the proportion of solid to fluid be duly preserved in the ingesta, and the food composed of wholesome alimentary principles only, in a fair proportion, the balance between the ingesta and the ejesta being moderately well preserved, the sensation of thirst and the necessity for large potations would seldom, if ever, recur. A close examination of the habits of diet among individuals in our own circle of observation, has led us to the conclusion, that the most robust and active consume from twenty to twenty-four ounces of dry material, and from sixty to eighty ounces of fluid daily. The quantity and proportion are subject to great variations, both within and without these limits; but the most frequent error committed, particularly among females, would appear to be an excess of liquid as compared with solid food. It is also unquestionably true, that an inordinate quantity of fluid. received into the system is less injurious, in consequence of the almost incredible rapidity with which, under favorable circumstances, the excess transpires.

v. AGE. For reasons before alluded to, the proportionate quantity of food required by the system at different ages differs considerably. During the periods of infancy and growth, the increment of the tissues, the additional loss of caloric, owing to increased surface in proportion to the bulk of the body, and the very great comparative muscular activity in youth, are so many causes in operation to demand a greater proportionate quantity of nourishment. Physiological considerations lead us to infer that a greater proportion of water to dry matter, and of non-nitrogenized to nitrogenized aliment, is demanded in the earliest periods of life. The

nourishment requires also to be well adapted to the digestive powers, hence the earliest food is furnished ready prepared by the nurse. A principle laid down by Lord Bacon seems to apply to this part of the subject, that it is a general law of organized nature, for those species and individuals that are slow in attaining maturity to live the longest, nature finishing her periods in larger circles. If this be admitted, an over nutritious diet during the period of growth may have the injurious effect of bringing the constitution forward too rapidly. At the same time, every practical man will agree with Dr. Pereira that,

"Of the ill consequences of defective nutriment we have, unfortunately, too many instances continually presented to our notice. Irritable bowels or diarrhea, tumid abdomen, mesenteric disease, wasting, and fever, are the ordinary and obvious effects. They frequently follow the continued use of pea-soup and potatostews, dishes which are in common use at poor-houses and other establishments for pauper children. Scrofulous and strumous diseases, marasmus, rickets, distortions, and pot bellies, so commonly met with among children of the poor, are referrible, in part at least, to food defective either in quantity or quality, or perhaps in both. I think it will be found that more than two thirds of pauper children are strumous. They derive this condition in part, perhaps, from hereditary tendency; but partly also, as I believe, from defective nutriment. To the same cause also is ascribable their inferior development. If the children in poor-houses be examined, they will be found for the most part, smaller and shorter for their age, more frequently distorted, and more readily fatigued, than the children of the middling and higher classes." (pp. 473-4.)

In adult life, in so far as the habits and locality of individuals are stationary, there is greater propriety in establishing fixed rules of diet than in the periods of development. A balance between decay and reparation exists, and probably during many successive years these processes are pretty uniform in degree. With change of locality, of season, and of habits, variations both in the quantity and quality of sustenance are required, but in the ordinary routine of life these may be kept within very moderate limits. As age advances the change of matter takes place more slowly; the powers of the body and the capability of labour and exertion, and in a proportionate degree the appetite for food decreases. We have estimated the quantity of aliment, and the proportion of dry to liquid material, consumed habitually by several old persons in good health. It varies from forty to sixty-five ounces, and the solids, but more particularly the nitrogenized alimentary principles, are more than proportionably diminished. An old lady of ninety, now living, walks about a mile daily, and enjoys uninterrupted good health with the possession of all her faculties; her daily diet is, upon an average, five ounces of solids and thirty-two ounces of drink, including eight ounces of porter and two glasses of wine. The cases of longevity published confirm these observations, and under every practitioner's eye, individuals of both sexes, who have arrived at a considerably advanced age, glide along the stream of life in the enjoyment of health, upon a very moderate supply of nutriment. So long as the supply and the expenditure as nearly as possible balance each other existence continues. It is a common expression applied to a bed-ridden octogenarian "he lives upon as little as would feed a sparrow." Let the balance be disturbed and existence is cut off. An increased quantity of nutriment destroyed old Parr, and two ounces in addition to his daily solid food nearly killed Cornaro. Many old men are prematurely cut off by exhaustion, "their spirits lead them beyond their