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in a physiological point of viewthe only one really implicated-with scarcely any results at all. No one doubts that Food is a physiological question, inasmuch as it relates simply to an organism. Nevertheless, it has fallen into the hands of the chemists; and our treatises, text-books, and even popular works, have been encumbered by hypotheses which may amuse speculative ingenuity, but furnish very little positive result. Against this vice of Method, and this misdirection of valuable labour, a voice should energetically be raised. The error is not a speculative error, simply: it is one carrying important consequences; it either leads physicians and farmers into serious mistakes, or leads them to throw up scientific guidance in disgust, because the hypothesis, so convincing on paper, turns out stubbornly irreconcilable with fact. Let us not, however, be misunderstood. In declaring the chemical hypotheses on the subject of Food to which Liebig, Dumas, Boussingault, Payen, and others, have given the sanction of their names, to be more of an encumbrance than an illumination, there is no idea of undervaluing their labours. All real work is important, no genuine research is unworthy of our gratitude; but it is one thing to reverence power, and respect the work achieved, another thing to assign the nature and position of that work. With regard to the vast chemical researches into the subject of Food which have occupied a quarter of a century, it seems to me that their value has been almost exclusively chemical, and only in an indirect and limited degree physiological. Hence, in spite of the unanimity and apparent precision observable in the analyses and hypotheses offered by chemists, no important practical results have been attained, not a single alimentary problem has been solved by them.
There may be readers who, failing to see the ground of this distinction between chemical and physiological investigations, will not understand the importance I attach to it; but they will perhaps come round to my point of view before this essay reaches its close. The chemists,
whatever we may think of them, will continue their labours, analysing, weighing, experimenting, and propounding hypotheses; and it is right they should do so: all honour and success to them! But if the question of Food is to receive any practical solution, it must no longer be left in their hands; or only such details of it left in their hands as properly belong to them. It must be taken up by physiologists, who, while availing themselves of every chemical result, will carry these into another sphere and test them by another Method. Not a step can the physiologist advance without the assistance of the chemist; but he must employ Chemistry as a means of exploration, not of deduction-as a pillar, not a pinnacle-an instrument, not an aim. The chemist may analyse fat for him; but he, on receiving this analysis, will request the chemist not to trouble him with hypotheses respecting the part played by fat in the organism for although the chemist may accurately estimate the heat evolved in the oxidation of so much fat, the physiologist has to do with a vital laboratory, extremely unlike that in which the chemist works, and he has to ascertain how the fat comports itself there.
Alimentary substances are substances which serve as nourishment; but a great mistake is made when it is imagined that their nutritive value can chiefly reside in the amounts of carbon, nitrogen, hydrogen, oxygen, and salts, which they contain; it resides in the relation which the several substances bear to the organism they are to nourish. Music is not harmonious to the deaf, nor is colour splendid to the blind. The substance which nourishes one animal affords no nourishment to another, nor will any table of “nutritive equivalents," however precise, convince us that a substance ought to nourish in virtue of its composition, when experience tells us that it does not nourish, in virtue of some defective relation between it and the organism. That one man's meat is another man's poison" is a proverb of strict veracity. There are persons, even in Europe, to whom a muttonchop would be poisonous. The cele
brated case of the Abbé de Villedieu is a rare, but not unparalleled example of animal food being poisonous : from his earliest years his repugnance to it was so decided, that neither the entreaties of his parents nor the menaces of his tutors could induce him to overcome it. After reaching the age of thirty, on a regimen of vegetable food, he was over-persuaded, and tried the effect of meat soups, which led to his eating both mutton and beef; but the change was fatal plethora and sleepiness intervened, and he died of cerebral inflammation.* In 1844, a French soldier was forced to quit the service because he could not overcome his violent repugnance and disgust towards animal food. Dr Prout, whose testimony will be more convincing to English readers, knew a person on whom mutton acted as a poison: "He could not eat mutton in any form. The peculiarity was supposed to be owing to caprice, but the mutton was repeatedly disguised and given to him unknown; but uniformly with the same result of producing violent vomiting and diarrhoea. And from the severity of the effects, which were in fact those of a virulent poison, there can be little doubt that if the use of mutton had been persisted in, it would soon have destroyed the life of the individual." Dr Pereira, who quotes this passage,† adds, "I know a gentleman who has repeatedly had an attack of indigestion after the use of roast mutton." Some persons, it is known, cannot take coffee without vomiting; others are thrown into a general inflammation if they eat cherries or gooseberries. Hahn relates of himself that seven or eight strawberries would produce convulsions in him. Tissot says he could never swallow sugar without vomiting. Many persons are unable to eat eggs; and cakes or puddings having eggs in their composition, produce serious disturbances in such persons: if they are induced to eat them under false assurances of no eggs having been
employed, they are soon undeceived by the unmistakable effects.
Under less striking forms this difference in the assimilating power of different human beings is familiar to us all we see our friends freely indulging, with benefit instead of harm, in kinds of food which, experience too painfully assures us, we can eat only with certain injury. To this fact the attention of parents and guardians should seriously be given, that by it they may learn to avoid the petty tyranny and folly, of insisting on children eating food for which they manifest repugnance. It is too common to treat the child's repugnance as mere caprice, to condemn it as "stuff and nonsense," when he refuses to eat fat, or eggs, or certain vegetables, and "wholesome" puddings. Now, even a caprice in such matters should not be altogether slighted, especially when it takes the form of refusal ; because this caprice is probably nothing less than the expression of a particular and temporary state of his organism, which we should do wrong to disregard. And whenever a refusal is constant, it indicates a positive unfitness in the Food. Only gross ignorance of Physiology, an ignorance unhappily too widely spread, can argue that because a certain article is wholesome to many, it must necessarily be wholesome to all. Each individual organism is specifically different from every other. However much it may resemble others, it necessarily in some points differs from them; and the amount of these differences is often considerable. If the same wave of air striking upon the tympanum of two different men will produce sounds to the one which to the other are inappreciable-if the same wave of light will affect the vision of one man as that of red colour, while to the vision of another it is no colour at all, how unreasonable is it to expect that the same substance will bear precisely the same relation to the alimentary canal of one man as to that of another! Experience tells us
* Journal de Medicine. Août 1760, quoted by LUCAS, De l'Hérédité, who is the authority for the next statement.
+ PEREIRA: Treatise on Food and Diet, p. 242.
that it is not so. A glance at the animal kingdom reveals the striking differences manifested by two closely allied organisms in their capability of assimilating the same substance. There are two species of Rhinoceros, the black and the white. The black species feeds on the graceful, but deadly, plant, Euphorbia candelabrum, and converts it into its own substance; but if the white species happen to eat thereof, it is inevitably poisoned. The Herbivora are divided into two classes, the first subsisting on a variety of plants, the second on one kind only. But even the various feeders will not touch certain plants eagerly devoured by others: thus the horse passes over almost all the cruciferæ; the ox all the labiates; goats, oxen, and lambs refuse almost all the solaneæ; and the poisons are food to many, the rabbit devouring belladona, the goat hemlock, and the horse aconite. The dog will feed on bread, or biscuit, which his ancestor the wolf would starve rather than touch. The cat, although preferring animal food, will eat bread and milk, which the tiger will not look at.
We have brought these facts forward for the sake of giving distinct relief to the importance which must inevitably belong to physiological considerations in every question of Food; and to indicate the necessity of fixing our attention on the organism to be nourished, rather than on the chemical composition of the substances which nourish it. When we are building a bridge, or making a machine, we can accurately guide ourselves by estimates of the strength of the wood and iron, because these substances do not lose their properties under new arrangements; but in building the mysterious fabric of the body, we have little or no guidance from our estimates of the properties of substances out of the body, because the body itself is an important factor in the sum, acting on the substances as well as acted on by them, annulling or exalting their properties in a way quite peculiar to itself. And it is because this has been overlooked, or not sufficiently estimated,
* MULDER: Chemie, 2d edit.
that our text-books are at once so precise, and so erroneous. Open almost any work on Physiology or Organic Chemistry, and you will meet with expositions of the theory of Food, and the nutritive value of various aliments, which are so precise and so unhesitating in their formulæ, that you will scarcely listen to us with patience when we assert that the precision is fallacious, and the doctrines demonstrably erroneous. Nevertheless we hope, before concluding, to convince you that Chemistry is itself in too imperfect a condition to give clear and satisfactory answers to its own questions in this direction-as Mulder and Lehmann frankly avow*
and further, that Chemistry, even supposing it to be perfect, must ever be incompetent to solve physiological problems, to which, indeed, it must always afford indispensable aid, without hope of doing more.
Vital processes depend on chemical processes, but are not chemical, and cannot, therefore, be explained by Chemistry. There is something special in vital phenomena which necessarily transcends chemical investigation. We need not pretend to settle what vitality is, or on what the speciality of its phenomena ultimately rests, to be assured that it is something quite unlike what goes on in our laboratories, and demands other tests than those furnished by Chemistry. The philosophic poet warns
and such appeal, from higher to lower, is the appeal of Physiology to Chemistry. No analysis of a nerve will ever throw light on Sensibility; no arrangement of chemical formula will explain the form and properties of a cell. You may take a mechanism to pieces, and explain by physical laws the action and interaction of each wheel and chain; but you cannot take a tissue to pieces, and from the elements deduce its properties. If an overwhelming illustration of this obvious truth be needed, we may find it in the ovum of an animal:
Versuch einer Physiol. Chemie. LEHMANN: Lehrbuch, d. Physiol.
here is a microscopic sphere, composed of substances well known to chemists, which contains potentially an animal, and will reproduce not only the form, features, stature, and specific attributes of the parents, but also many of their acquired habits, tendencies, and tricks; has Chemistry, in the whole extent of its domain, anything analogous to this? Can Chemistry furnish us even with an approach to an explanation of it? Chemical analysis inay conduct us to the threshold of Life, but at the threshold all its guidance ceases. There, a new order of complications intervenes, a new series of laws has to be elicited. Chemistry confesses its inability to construct organic substances, or even to say how they are constructed; it can, at present, only say of what they are constructed. This being so, it is clear that every attempt to explain chemically the nutritive value of any aliment, by an enumeration of its constituents, must belong to what Berzelius admirably styles "the physiology of probabilities."
There is one cardinal rule which can never be violated with impunity, and which is, nevertheless, perpetually violated in our gropings towards the light. It is this: Never attempt to solve the problems of one science by the order of conceptions peculiar to another. There is an order of conceptions peculiar to Physics, another peculiar to Chemistry, a third peculiar to Physiology, a fourth peculiar to Psychology, a fifth peculiar to Social Science. While all these sciences are intimately related, each has its sphere of independence which must be respected. Thus Chemistry presupposes Physics, and Physiology presupposes Chemistry; but no physical laws will explain chemical phenomena, no chemical laws will explain vital phenomena; nor, conversely, will Chemistry solve physical problems, nor Physiology solve chemical problems. In every vital process physical and chemical laws are implied, and the knowledge of these becomes indispensable; but over and above these laws, there are the specific laws of Life which cannot be deduced from Physics and Chemistry.
An illustration drawn from social science may serve to render this
canon intelligible, and at the same time to uproot a widespread fallacy. Few errors have gained more general acceptance than that which declares the Family to be the perfect type of the State, and which would regulate polity by domestic rules. A paternal government, in which the monarch is the head of the family; and a social government, in which all men are united as brothers, are the two ideals of absolutists and socialists, who are pitiless in scorn of all other political schemes. When we see how a wellconducted household is harmoniously governed, each member fulfilling his proper office, and each assisting all; when we see how the farmer administers his affairs without any one to question his absolute will; the idea of so managing a nation naturally suggests itself, for What is a nation but an extension of the family? ask the theorists. I answer, the Family is specifically different from the Nation: it is no type of the State, because, not to mention other points, it has the bond of personal affection, and the bond of personal interest, which two puissant influences can never operate to anything like the same extent on the State. The father dearly loves his children, and his despotism may be absolute because it is truly paternal, his tender vigilance and forgiving love will soften all the harshness of absolute rule. But no philanthropist will be romantic enough to expect that king or kaiser can by any possibility feel this affection for his subjects; and thus one essential element of the family disappears. Again, the father's personal interest is bound up with his administration (as the farmer's is), and every false step he makes will be made feelingly evident to him. But the sovereign's personal interest is not in any such manner directly bound up with the goodness of his administration; if he can keep secure upon his throne, if neither revolutions nor assassins are provoked, it can make little difference to his welfare if the streets are filled with lamentations, and the battlefield with corpses. And even supposing him to be tender-hearted and conscientious, really desirous of the good of his subjects, yet his own personal interest is not so directly and
obviously bound up with theirs as that of the father's with his household. Thus, on the supposition that the despot is the best and wisest of men, and his subjects are really desirous of universal brotherhood (two tremendous assumptions always quietly made), the Family could offer no proper type of the State, because the two most puissant elements in the Family must be wanting in the State. The application of the canon just laid down is easily seen while, on the one hand, the Family must necessarily enter into the State, which is in truth an aggregation of families, it can never furnish the typical laws for the State, because the actions of individual men cannot be the standard for the actions of masses, and the mere aggregation of families brings about such a complication of interests, passions, and opinions, that a totally new set of relations is evolved. Thus precisely as Polity presupposes Domesticity, but is not embraced by it, precisely as the State is dependent on the Family, and is, nevertheless, belonging to a higher jurisdiction, so does Physiology presuppose Chemistry, but is not included in it, cannot be regulated by its laws. Domestic life furnishes the basis for political life, as chemical actions furnish the basis for vital actions.
Whatever the future progress of Chemistry may effect in the way of simplifying physiological problems (and no one doubts that it must greatly aid us), there is one radical distinction which must ever keep the two sciences separate. It is this: Chemical laws are quantitative, because chemical actions are definite combinations; whereas physiological laws can never become quantitative, but only qualitative, because vital substances are indefinite in composition; that is to say, while chemical substances are formed by combinations of unvarying quantities, never more, never less, so much acid to so much base always forming the same salt, so many atoms of one substance always uniting with so many of another to form a third; the substances on which vital actions specially depend are never precisely and accurately definite; they vary in different individuals, and at different ages of
the same individual; and as every variation in composition necessarily affects the properties of each substance, it is impossible that such actions can be reduced to those exact quantitative formulæ on which Chemistry is founded. Chloride of sodium is the same substance, having precisely the same composition and properties, whether taken from the sea, from the earth, from the plant, or manufactured in the laboratory. But nerve-tissue is never precisely the same in two men; the blood of no two men is precisely alike; the milk of no two women is identical in composition-they all vary (within certain limits), and sometimes the variation is considerable. It is on this, as I have elsewhere maintained, that depends what we call the difference of "temperament," which makes one twin so unlike his brother, and makes the great variety of the hu
We have now done with the generalities which it was needful to explain before approaching the question of Food. If the reader's assent has been gained, he will see that from the radical incompetence of Chemistry to settle any true physiological question whatever, all the laborious efforts of later years have been barren, or nearly so, as regards the important subject of Food, because they have been only chemical reasonings on Physiology. Plausible and brilliant as some of the theories have been, they are all at fault when reduced to practice. They have gained general acceptance, because of the simplicity with which they seemed to solve abstruse problems; and the human mind is so eager to have explanations, that any logical plausibility is sure to captivate it.
Of all current hypotheses on this subject, none claims a closer scrutiny than that which_Liebig has made familiar to all Europe, and which, winged by the two qualities of simplicity and plausibility, has been carried into the lecture-room and study, where it continues to hold its place, in spite of the growing conviction that it is untenable. Liebig divides Food into two classes. The first is Plastic, or tissue-making, and comprises the organic substances