in southern climates contain much less carbon than the train-oil eaten in polar regions, would be a tolerable example, if only fruits were eaten in the one; but the Sicilian and Neapolitan eats more oil than the Swede, and his macaroni is a highly carbonised substance; and the Hindoo subsists on rice and butter-substances highly carbonised, and classed as chiefly respiratory, furnishing in superabundance that very heat which his climate renders so undesirable. According to theory, the Hindoo should eat very little non-nitrogenous food, and be content with plastic substances, since he wastes his tissues in daily labour, but does not stand in need of any surplus heat; whereas, according to fact, he eats very little nitrogenous food, and a great deal of " heat-making" food. And this damaging fact is brought into even greater relief by the experiments of Messrs Lawes and Gilbert (who nevertheless do not seem to oppose the theory), as thus recorded by them: The weather, during part of the period of this second series of experiments, was exceedingly hot; from this several of the animals suffered considerably; and some, either from this or other causes, became quite ill, and died, or were 'killed to save their lives.' Nevertheless it is seen that there was upon the whole a larger amount of respiratory food consumed in relation to weight in this series than in the previous one, during the cooler season. ." Against such evidence as this, the respiratory nature of non-nitrogenous food is more than equivocal.

It is a fact that, in cold countries, fat and oil are greedily devoured; and it is the most striking fact that Liebig can adduce in his favour. But we have yet to learn that fat is simply so much" combustible" material. The demand for fat in cold countries may arise out of various conditions. Increase of cold causes increased activity of respiration, and increased activity of muscular exertion. These cause a greater waste of tissue; consequently increased repair is needed;

*Report, p. 340.

and as fat is indispensable to such repair, we can therein see one source of the demand for fat. Besides subserving this end, fat will also assist animal heat in virtue of its low conducting power retarding the loss of temperature. Oil the body externally, and you efficiently protect it from cold. The reader will bear in mind, that we are not disputing the position that fat is burned in the body, or that it is not one important source of animal heat; far from it; the point disputed is, whether fat is only a heat-producer, and the demand for it in cold countries only a demand for combustible material. On this point it is well worthy of remark, that Schmidt's researches prove fat to be less easily combustible in the blood than the carbo-hydrates, and even than the albuminates, so that the Hindoo, in his rice, eats a substance more immediately oxidisable in the blood than the tallow eaten by the Esquimaux; and if fat be demanded in cold countries, only to supply animal heat, that supply would be better afforded by starchy substances, were the chemical hypothesis the true one.

What has been already said will perhaps suffice to show how untenable a position is that which denies nutritive value to fats, sugars, starch, water, &c., throwing the whole burden of nutrition on the albuminous substances; it may complete the overthrow of that position if I now show that while the fats are tissue-makers, and heat-producers, the albuminates are heat-producers, and tissue-makers. No one doubts that heat is evolved in the chemical changes which albuminates undergo; the doubt raised can only be as to the amount. Liebig says:

"If the combustible elements of the

plastic constituents of food served for the production of heat, the whole amount of the substances consumed by the horse in his hay and oats, by the pig in its potatoes, could only suffice to support their respiratory process, and consequently their animal heat, in the horse for 4 hours daily, in the pig for 4 hours daily; or if confined to plastic food, they

would require to consume five or six times as much of it. But even in this last case it is exceedingly doubtful whether these substances, considering their properties, would in the circumstances under which they are presented to oxygen in the organism produce the necessary temperature of the body and compensate for the loss of heat; for of all organic compounds, the plastic constituents of food are those which possess in the lowest degree the properties of combustibility, and of developing heat by their oxidation."*

Every chemist would echo this statement, because Chemistry teaches that of all the elements of the animal body nitrogen has perhaps the feeblest attraction for oxygen; not only so, but it even deprives other substances, with which it combines, of their tendency to unite with oxygen. Phosphorus, for example, has an eager affinity for oxygen, as we know from its ready combustibility in atmospheric air at ordinary temperatures; but when combined with nitrogen its combustibility is so difficult that it can only be effected at red heat and in oxygen gas. Liebig hence concludes, and from the chemical point of view is justified in concluding, that precisely the same relations are preserved in the blood. The albuminous (nitrogenous) bodies have, he says, but a very slight affinity for

oxygen.

"If the albumen of the blood, which is derived from the plastic portion of the food, possessed in a higher degree the power of supporting respiration, it would be utterly unfit for the process of nutrition. Were albumen as such destructible, or liable to be altered in the circulation, by the inhaled oxygen, the relatively small quantity of it, daily supplied to the blood by the digestive organs, would quickly disappear. As long as the blood contains, besides albumen, other substances which surpass it in attraction for oxygen, so long will the oxygen be unable to exert a destructive action on

this the chief constituent of the blood; and the significance of the non-nitrogenous food is thus made clear."

It is not surprising that a theory so logical should have gained general acceptance; and as a specimen of chemical reasoning on physiological

*LIEBIG, Chemical Letters, 372.

problems it is very brilliant. Nevertheless, when we study what takes place in the organism, we find direct and unequivocal contradiction given We find on the one hand that races to each separate clause of the theory. of men live for considerable periods on animal flesh alone-and this, being the flesh of wild animals, contains very little fat, even in comparison with butchers' meat, which does not contain much; yet these men lead an active life, respire vigorously, and need abundant animal heat; so that nitrogenous food must to them be amply sufficient for the temperature of the body. On the other hand, we find races of men living always on vegetable food, containing little nitroabundance of animal heat is not gen, and in climates where a superneeded; so that to them non-nitrogenous food must be sufficient for the only do these massive facts overchief supply of nutrition. And not power the chemical hypothesis, but even Chemistry itself, when interrogating the facts of organic life, disof albuminates for oxygen, out of the covers that, however weak the affinity blood, its affinity, in the blood, surpasses that of fat. Schmidt, to whose experiments science is so deeply indebted, found that on feeding cats now with flesh alone, and now with fat alone, or with much fat and little flesh, the albuminates were always more rapidly destroyed than the fat, which was at first stored up in the body to be afterwards gradually oxidised; and these experiments are confirmed by Persoz in fattening geese with maize: the blood of the fattened geese was very rich in fat, but notably impoverished in albumen; the quantity of muscular substance was much diminished, and when the fattening was rapid the weight of the whole body was absolutely diminished.†

To the chemist these results will

be paradoxical, if not inconceivable, and he will doubtless point to the well-ascertained fact that in starvation it is the fat which disappears first, and the muscles only yield up their elements to destruction when most of the fat has been oxidised.

+ LEHMANN, Physiol. Chemie, iii. 386.

This point has already been dwelt on by us when treating of HUNGER and THIRST. All that can here be said is, that it needs to be reconciled with the seemingly contradic tory facts; and when we come to understand more of the conditions of organic substances in various parts of the organism, we may understand how it is that fat which is scarcely oxidisable in the blood may be readily oxidisable in the tissues. How slow we should be in conclud

ing from what takes place out of the organism, to what takes place in it, is taught us in a hundred physiological facts: thus the fat which can be decomposed into fatty acid and glycerine by means only of the most energetic acids and alkalis in the laboratory, is thus changed in the organism by the pancreatic juice, which has but feeble chemical properties, but which brings about the result by means of an organic substance acting as a ferment.*

We might multiply to a great extent the objections which present themselves to Liebig's theory of Food, but those already stated are sufficient to show that it is erroneous in every particular, in spite of its logical dependence and plausibility. The only extensive series of experiments on feeding, with which we are acquainted, as immediately serviceable, are those instituted by Messrs Lawes and Gilbert, and to them the reader is referred; because, although they are by no means such as, from the nature of the experiments, can give Physiology any accurate data, they are valuable as practical results, and utterly destructive of Liebig's theory. They show among other things that "although pigs were satisfied to eat a smaller proportion of food in relation to their weight, in those pens where the proportion of nitrogen was comparatively large, yet the proportion of increase to the food consumed was less than where the amount of non-nitrogenous food consumed was greater." And further, that "whilst the non-nitrogenous substance consumed to produce 100 lb. increase in weight is very

p. 391.

nearly equal in the two series; yet that of the nitrogenous constituents varies in the proportion of from three to two!" Again: "In the fourth pen where there was by far the largest amount of nitrogen consumed the animals lost weight; and in the other three pens the productiveness of the food is in the inverse order of the amounts of nitrogen taken in the food. Indeed, we believe that an unusually high percentage of nitrogen in succulent produce is frequently a pretty sure indication of immaturity and innutritious qualities." Summing up the results of their whole series of experiments, the largest yet instituted, they declare that it is 66 their available non-nitrogenous constituents rather than their richness in nitrogenous ones that measure both the amount consumed to a given weight of animal, in a given time, and the increase in weight obtained." + And they refer to the instinctive preference given by the under-fed labouring classes to fat meat, such as pork, over those meats which are leaner and more nitrogenous.

Long as we have tarried over this part of our subject, the time will not have been misspent if it have clearly impressed the conviction that nitrogenous food is not the exclusively plastic food, and that per-centages of nitrogen afford no nutritive standard -the conviction that Liebig's classification is fundamentally and circumstantially erroneous and dangerousand the conviction that Chemistry is wholly incompetent to solve the problem of Food.

As soon as we relinquish the seductive notion of physiological deduction from chemical laws, and place ourselves at the proper point of view, namely, that of the organism to be nourished, our classification of Food speedily falls under two main divisions - Inorganic and Organic substances; and, doubtless to the reader's surprise, the Inorganic turns out to be the more important of the two, supposing always that a question of degree can lawfully be entertained where both kinds are indispensable.

We are not, indeed, accustomed to consider minerals as food, or water as highly nutritious; but that is because we are not accustomed to consider the subject with the needful accuracy. Tell the first man you meet that water is on the whole more nutritious than roast-beef, and that common salt, or bone-ash, is as much an edible as the white of egg, and it is probable that he will throw anxious glances across the streets to assure himself your keeper is at hand. Make the same statements to the first man of science you meet, and the chances are, that he will think you very ignorant of organic chemistry, or that you are playing with a paradox.* Nevertheless, it is demonstrably true, and never would have worn the air of a paradox, if men had steadily conceived the nature of an alimentary substance. That is an aliment, which nourishes; whatever we find in the organism, as a constant and integral element, either forming part of its structure or one of the conditions of vital processes, that, and that only, deserves the name of aliment. But we have been seduced from this simple conception, partly by vain endeavours to ascertain in analyses of food and excreta what are the truly nutritive substances, and partly by misconceptions of the processes of Nutrition.

Of these latter there is one, widely spread, which declares, that while Plants are able to nourish themselves directly by inorganic materials furnished them in the air, earth, and water, Animals are incapable of thus drawing nourishment from inorganic materials, but depend solely on the organic materials prepared for them by Plants. The Plants feed on minerals, the Herbivora feed on Plants, and the Carnivora on the Herbivora. The cycle is complete, the symmetry of nature is perfect. One feels a kind of pity in having to

disturb so elegant a formula; yet the truth must be told, and the truth is, that not a single statement so expressed is altogether correct. Certain it is that Plants can, and do, convert inorganic substances into the organic, but it is not less certain that this power is very limited, all except the simplest (perhaps not even these) needing organic principles to be yielded by the soil in which they grow. This destroys the distinction between Plants and Animals,, by showing that both, more or less, depend on organic substances. It is this inability in Plants to dispense with organic matter that renders manure necessary.+ While so much is certain, the general assumption is, that Animals are altogether incapable of converting any inorganic materials into organic; and are rigorously dependent on Plants for every organic substance met with in their bodies. This assumption seems to me wholly unwarranted by any decisive knowledge yet obtained. The main argument on which it rests, namely, that unless organic substances be given in the food, and in certain proportions, the animal perishes of starvation, has no longer any coercive force when we reflect that starvation as inevitably follows if inorganic substances be withheld. Organic substances-of a low order it is true-have been manufactured by the chemist out of inorganic substances; and if alcohol and urea are already capable of being made in the laboratory, I see no reason for supposing that even more complex substances may not be made in the vital organism, the seat of such incessant chemical transformation.§ Be this as it may, the distinction between Animals and Plants falls to the ground when we see that Plants do require organic substances, and that ́Animals do nourish themselves with inorganic substances taken directly from earth,

air, and water. We hew salt from the quarry to cast it in handfuls upon our stews and soups, or in pinches on our meat and potatoes. We draw water from the spring to drink; and, like the plants, we draw gases (oxygen, perhaps also nitrogen) from the air, to enter into those various combinations without which no life is possible. It may be unusual to call these nutritive principles, but if unusual it is not unscientific. If "to nourish the body" mean to sustain its force and repair its waste-if food enters into the living structure--and if all the integral constituents of that structure are derived from food-there can be nothing improper in designating as nutritious, substances which have an enormous preponderance among the integral constituents. People who think it paradoxical to call water Food, will cease their surprise on learning that water forms two-thirds of the living body; and they will perhaps cease to marvel at the nutritive value here attributed to minerals, on learning that when all the water is eliminated, and the solids which form the remaining one-third are analysed, they are found to contain no less than one-third of mineral substances which remain as ashes. Nor must the presence of these mineral substances be regarded as accidental or unimportant. They are constant, constituent, essential. Blood is not blood without its salts and iron; bone is not bone without its phosphates; muscle is not muscle without its salts.

Let us glance at one or two of these inorganic elements; and, first, at phosphate of lime. There is not a single humour, nor a single tissue in the body, which is without a certain proportion of this salt. By removing it, the integrity of the tissue is destroyed, and all characteristic properties as infallibly altered as if the organic elements were removed. If the needful quantity be withheld or withdrawn, the bones become weakened, as we see in pregnant women, whose fractured limbs are with diffi

culty healed (sometimes not at all), simply because their phosphate of lime has been diminished by the demands of the child. A similar effect is noticeable in infants during teething, a period when the "rickets" often make their dreaded appearance. But still more fatal is the effect of withholding this salt from the food, as we learn in the striking experiments of Chossat, who withheld it from pigeons, allowing them to eat no more than was contained in the grain and water on which he fed them they all perished miserably, after attacks of diarrhoea and softening of the bones.*

The absolute necessity of a supply of inorganic materials in Food is further illustrated in one of the experiments of Messrs Lawes and Gilbert, who note that

"the pigs in pen 5, where Indian meal alone was given, had become affected necks, their breathing and swallowing with large tumours breaking out on their becoming at the same time difficult; we, in order to test the question as to whether this arose from the defect of nitrogen or from other causes, supplied them with a trough of mineral substances: they soon recovered from their complaint, and eventually proved to be among the fattest and best of the entire series of

pigs; at least a dealer in pork, with a practised eye, purchased, by preference, one of these animals from among the whole set of carcasses. The mineral mixture supplied to them was composed of twenty parts coal-ashes, four parts common salt, and one part superphosphate of lime; and for it they seemed to exhibit considerable relish." +

The point is forcibly put by Liebig:

"In the two preceding letters, there has been ascribed to certain constituents of seeds, tubers, roots, herbs, fruits, and flesh, the power of supporting the processes of nutrition and respiration; and it will appear as a very striking contradiction when it is stated, that no one of these substances by itself, neither caseine alone, nor the substance of muscular fibre, nor the albumen of eggs or of the blood, nor the corresponding vegetable