4. The amylaceous principle. This is one of the most abundant constituents of vegetable food, occurring in quantities which vary from 3 to 72 per cent. Sago, tapioca, arrowroot, cassava, tous-les-mois, potato-starch, salep, rice-starch, &c., are here treated of separately as articles of diet, consisting almost entirely of starch. This principle is regarded in the same point of view as sugar, both by Prout and Liebig, except that it forms a necessary part of human food,-may be employed in much larger quantities than sugar, and its use persisted in for an unlimited period. According to Liebig, when in excess, under favorable circumstances, it contributes to the formation of fat, but is incapable of transformation into the azotized materials of blood. Both sugar and starch are easily digested in the human stomach.

5. The ligneous principle. This is introduced rather in deference to an opinion of Dr. Prout than from a conviction in Dr. Pereira's mind, that it is capable of yielding nutriment to man. It is true that it forms the appropriate food of various insects, and of some of the lower animals, and when reduced by various processes, it is said to form a substance analogous to the amylaceous principle. But many of the facts relating to the use of bark and wood as food, by the Laplanders and other tribes, may be accounted for by the formation and the diffusion of starch through every part of the plant, in the autumnal sap. So that starch may in reality be the nutritive principle of bread made of bark and wood. The ligneous matter of our ordinary vegetable foods is evacuated with the fæces, as indigestible refuse, being sometimes of use as a mechanical stimulus to the bowels, as the bran of wheat; and sometimes injurious, as the husks of fruit.

6. The pectinaceous principle. Vegetable jelly. This includes pectine and pectic acid, one or both being contained in most pulpy fruits, as currants, apples, oranges, and in many vegetables, as artichokes, carrots, and turnips. Unripe fruits contain but a very small quantity. The dietetical properties of vegetable jelly are very little known, but it is readily digested, and is probably slightly nutritive. Its components are carbon and the elements of water, plus oxygen, and like other principles of this nature, it is classed by Liebig as an element of respiration. Dr. Pereira remarks, that in consequence of the excess of oxygen in relation to hydrogen, the use of vegetable jelly may be to diminish the function of respiration. It is uncertain whether the tendency which fruits have to promote alvine evacuations depends upon this principle.

7. The acidulous principle. Dr. Pereira's reasons for admitting this, are, that vegetable acids constitute one of the most constant ingredients of our foods; that fruits and succulent herbs have been in use both in ancient and modern times, and vinegar from a very early period; and that the employment of vegetable acid appears, from various statements before us of the effects which result from complete and prolonged abstinence from vegetables and fruits, or their preserved juices, to be necessary for the preservation of health. The pure acids will not in every way supply the place of the natural juices, and all vegetable juices are not equally beneficial. Some of the acids, as the oxalic, tartaric, and gallic, form combinations with bases before they enter the circulation, and these compounds appear in the form of salts in the urine. Others, as the tartaric, malic, and acetic, suffer decomposition in their transit; their carbon

being converted into carbonic acid, and their salts appearing as carbonates in the urine. It will be observed that the principles already described comprise the saccharine group of Dr. Prout.

8. The alcoholic principle. This belongs to the oleaginous group of Prout. According to Liebig it is another element of respiration. Dr. Pereira, adopting the latter view, regards it, under some circumstances, as an alimentary principle. Its carbon and hydrogen act as fuel in the animal economy, and in cases of extreme suffering and exhaustion its "cautious and moderate dietetical use" has, on many occasions, proved invaluable. The use made of alcohol by coachmen to avoid "catching cold," and Captain Bligh's account of the good effects of a little rum served out in teaspoonfuls, in lessening the sufferings of himself and companions, arising out of the mutiny of the crew of the Bounty, are cited as examples.

9. The oily principle. Vegetable and animal foods contain fixed oils and fats composed of the well-known fatty and saponifiable principles. According to Liebig, these oily principles, composed chiefly of carbon and hydrogen, are incapable of forming the essential parts of blood; and, like other non-nitrogenized principles, they serve as fuel for the support of respiration. Dr. Prout holds, on the other hand, that, like sugar, they are convertible into most, if not all, of the matters necessary for the existence of animal bodies. But oily diet alone is incapable of supporting life; animals fed upon it exclusively soon die of inanition. The oily globules from the food appear to be conveyed into the blood, and to be deposited in the adipose tissue, or they contribute to the formation of the nervous tissues. The principal aliments of this class are fat, suet, marrow, butter, and olive and other vegetable oils.

Volatile oils form the material of flavour and odour of numerous productions of the vegetable kingdom employed at table either as aliment or as condiments; as of thyme, parsley, onions, &c. The oils are for the most part absorbed, and subsequently eliminated, without losing their characteristic qualities; or they may in part be burnt, and produce heat. 66 They stimulate but do not seem to nourish;" their principal effect being that of gratifying the palate.

10. The proteinaceous principle. This group differs from the albuminous alimentary class of Dr. Prout, in the omission of gelatinous substances. The dietetic properties of pure protein have not been ascertained, but its compounds form the plastic elements of nutrition of the German school. Protein is formed only in vegetables, the animal organism possessing the power of converting its various modifications into each other. Hence the importance of vegetables to animals as the exclusive source of the most essential material of their nutriment. The fibrin and albumen of blood, the substance of every variety of muscle, and of all the important viscera, the casein of milk, and accordingly the nutriment of the young, are equally dependent upon a supply of this principle. The organic material of the brain and nerves, being distinct in composition from that of all other animal tissues, is formed in the animal body only, and its formation takes place "from compounds of protein, either by the loss of some azotized compound, or by the addition of carbonized products, as fat." The proteinaceous food employed by man is derived both from animals and vegetables. In his infancy

from the caseum of milk, and in after life from the muscles, viscera, and fluids of animals; and from the seeds and other parts of plants. Animal fibrin is contained in variable quantities in the more usual articles of animal diet; for instance, in the muscle of beef, together with albumen, there is 20 per cent., in the sole 15 per cent., and in sweetbread 20 per cent. Fibrin speedily dissolves in the living stomach, and even in dyspeptics is regarded as of easy digestion: but, employed exclusively, it is incapable of supporting life. Animal albumen constitutes perhaps the most important part of animal foods. The white of eggs contains 15 per cent. Like the former substance, it is of easy digestion and highly nutritious. The gastric juice dissolves it, coagulating it in the first place, if liquid. Liebig regards it as the true starting point of the animal tissues; with the aid of air, of the oily matter of the yelk, and of iron, the whole being derived from it during the incubation of the chick. Yet animals cannot subsist on albumen alone, but refuse it and die of starvation when it constitutes their sole diet. Animal casein is distinguished from albumen and fibrin by its great solubility. As it occurs in milk it

is of easy digestion. Liebig asserts that no foreign substance is required to convert it into blood, and that it contains a much larger portion of the earth of bones in a very soluble form, than blood does; indicating how completely dependent the development of the vital organs in animals is upon the supply of a substance identical in organic composition with the chief constituents of blood. Milk contains from 1.52 to 4.50 per cent. As it occurs in cheese, this principle is of much more difficult digestion, requiring for its solution in the stomach as much as three and a half hours. The vegetable proteinaceous substances are also fibrin, albumen, and casein; the analyses of which do not differ from each other, or from those of the corresponding animal principles, more than two analyses differ of one and the same substance. Their nutritive powers are equal to those of the proteinized substances derived from animals. The quantities of these principles in vegetables are extremely variable; peas and beans, for instance, contain 14 or 15 per cent. of legumine or casein; rice, from 3 to 4 per cent. of fibrin or gluten; the dried juice of the carrot a little more than 4 per cent. of albumen; the potato 5 per cent. of albumen, and 055 per cent. of gluten. If proteinized principles be deficient in the food of herbivorous animals, nutrition is arrested; and carnivora in consuming the flesh and blood of herbivora consume in fact only the vegetable principles which have served for the nutrition of the latter. As Fordyce described it, before chemistry had determined the composition, even of water or air-"The lion may live on the horse, but the horse derives its nourishment from grass, and those animals which live on the flesh of such other animals as are sustained by vegetables may be considered as ultimately living on vegetable food."

18. The gelatinous principle. Dr. Prout regards gelatin as a modification of albumen, or, as "the least perfect kind of albuminous matter existing in animal bodies." This substance, as an article of food, is derived from isinglass, and from the skins, tendons, and bones of animals, and also from cellular membrane; differing considerably in its properties and its digestibility, as obtained from different sources. Gelatin differs from albumen in its chemical properties and composition, and for this and other reasons its nutritive uses cannot be identical with those of the

proteinized compounds. Liebig considers that gelatin is formed in the animal body from some of the compounds of protein, but, at the same time, that gelatinous food may contribute directly to the nourishment of the gelatinous tissues. Animals die of starvation if attempted to be nourished on gelatin alone. M. Donné tried its effects on himself; "at the expiration of six days he had lost two pounds' weight, and during the whole time was tormented with hunger, and suffered from extreme faintness, which was only alleviated after dining in the usual way." Still, the daily experience of the physician proves that gelatin, in conjunction with other alimentary substances, assists in nutrition.

12. The saline principle. Saline matters being essential constituents of the blood and of the organized tissues and secretions, they are necessarily component parts of our food, and among the most important, in a dietetical point of view, as entering most largely into the living solids and fluids, are common salt and the earthy phosphates. To these may be added the salts of potassa and the compounds of iron.

Although chloride of sodium is a constituent of many articles of food and of drink, yet these do not contain a sufficient quantity to supply the wants of the system; as a component of the blood, an excess or deficiency of this salt appears to affect the constitution of the blood-corpuscle, and from the salt of the blood the gastric juice derives the chlorine of its hydrochloric acid, and the bile obtains the sodium of its soda; the addition of salt to our food is therefore a necessary practice. The earthy phosphates are constantly present in the ashes of animal substances, and being necessary constituents of these, as well as of bones, they must be supplied to the system, and are accordingly component parts both of animal and vegetable food. Corn, potatoes, milk, eggs, and the flesh and blood of animals furnish, in fact, more than the demand, the excess being eliminated in the secretions. The salts of potassa are also derived both from animal and vegetable food, and all the nutritive plants contain compounds of iron, which element reappears in the blood and flesh of animals.

Our examination of the chapter of which the above is an abstract, induces us to suggest the question-what is an alimentary principle? It is manifestly not simply a proximate principle of organic substances, according to the meaning attached to that term by the chemists; although many of these are truly alimentary principles. Quinia is a proximate, but not an alimentary principle. Dr. Prout, who first made a specific application of the term, grouped several proximate materials together, to constitute one great alimentary principle. This is exemplified in the albuminous and the saccharine groups. Moreover, he holds that the diet of man, and of the higher classes of animals, to be complete, must contain more or less of all his " staminal principles;" this being illustrated in the case of milk, the only substance prepared by nature expressly for food, which contains water, a saccharine, an albuminous, and an oily matter; and again, in the food of the more perfect animals, composed, for the most part, of substances referrible to three if not to four of these staminal groups. So far, this may be considered a philosophical account of the essential constituents of food. But there is another point of view in which these principles may be regarded, viz., as identical in composition, and in the arrangement of their elements, with the materials that compose

the structures they are intended to produce or to nourish. Here Dr. Prout's arrangement fails, for there is no tissue in the animal system of which the saccharine principle is the prototype, and there are tissues which have no prototype in the food, as the nervous. The progress of discovery recently, has rendered this identity in the essential constituents of food, compared with those of the animal structures, much clearer; it has furnished new instances, and, in the school of Liebig, it has gone so far as to render it doubtful, whether the living tissues of the body are ever nourished otherwise than by the elements of which they are composed being introduced from without, in forms of combination more or less nearly allied to their own. If this doctrine were well established, there would be no question about the true basis of the science of dietetics. Dr. Pereira's" alimentary principles," however, answer neither the one nor the other of these descriptions. They appear to be compounds introduced into the digestive organs as aliment, and capable of being appropriated to any necessary, or even useful purpose, in the economy-a totally different affair; and although we are not disposed to quarrel with a name, the wisdom of the designation given to them, viewed as a whole, may be fairly doubted.

Dr. Pereira makes gum an alimentary principle distinct from sugar; not that both are essential to the nutrition of the body, but, as we read it, because gum may be employed as a dietetical and probably as a nutrient agent. Most complete have been the revolutions of opinion respecting this substance. For many years it was regarded as the most nutritious part of vegetable substances, and by some, as the only nourishment they afford; an opinion, supported by a fact, noticed by Fordyce, and quoted from him by many succeeding writers, that men have been nourished by "gum seneca" and water for many weeks, in caravans which had lost their way in the sandy deserts of Africa. Magendie's experiments, proving that animals fed on gum alone soon die of inanition, led to the totally opposite opinion, that it has no nutritive powers; and indeed it has been looked upon by some as serving no useful purpose in the economy. Liebig describes it, after passing the digestive organs, as fuel for combustion. Prout assigns to it the capability of being converted, within the economy, into some more essential nutritive compound, but of this we have no experimental proof. With respect to the story told by Hasselquist, the traveller above referred to, any opinion founded upon the use of a substance such as gum, in its crude state, and under the circumstances described, must be inconclusive. Gum senegal, in particular, is well known to differ from gum arabic, having a slightly bitter flavour. It has been said that an Arab can live upon six ounces of gum daily, but he takes it dissolved in milk, and recent experiments appear to show that gum arabic contains a small portion of azote.

Lignine is introduced upon the bare suspicion of its being a distinct principle capable of yielding nutriment to man. Pectine and pectic acid, again, have no very distinct nutritive properties. Even those materials of the ingesta, which appear to serve no other purpose in the economy but as fuel for combustion and the production of animal heat, taking no part in the nutrition of the vital structures, as taught by Liebig and his disciples, are still, while following Liebig's doctrine, separately regarded as alimentary principles; alcohol, for instance. On the other hand, some data are given, to render it probable, that the acidulous principle serves