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CHAPTER V.

ORGANIZED PRINCIPLES-DEFINITION--DR. PROUT'S OPINION OF THE
ORIGIN OF URIC ACID-UREA AND URIC ACID NOT FOUND IN
ANIMAL SUBSTANCES-NOR IN THE STOMACH-INCONVERTIBILITY
OF ORGANIZED PRINCIPLES-HIPPURIC ACID IN THE URINE OF
HERBIVOROUS ANIMALS-RELATIONS OF UREA AND URIC ACID-
LIEBIG'S OPINION OF THE ORIGIN OF UREA-EFFECT OF RESPI-
RATION-OF SLEEP-OF EXERCISE-OF FOOD-URINE OF CAR-
NIVOROUS AND HERBIVOROUS ANIMALS AND OF BIRDS.

It is not very easy to say what those substances are to which modern chemists have given the name of organized principles. It is a term used with little precision. At times I fancy that it is confined in its meaning to those principles employed in the construction of organized beings, such as albumen, fibrin, gelatin, &c. At other times it is used to include all products of organization.

In this work I would strictly confine the meaning of the term to those products of organized beings which are never met with out of the body, and which are not to be imitated by any artificial process. Such are albumen, fibrin, gelatin, uric acid, and, notwithstanding the experiment of

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how far organized principles are

convertible.

Some of them approach so near each other in chemical composition, that it is rather in their external appearance and their physical qualities, than in their elementary constitution, that we seek their distinction. Yet it is plain that nature has opposed strong barriers to that confusion which would result from a ready transition of one principle into another. So much is this the case, that the researches of organic chemistry seem to have been conducted almost with the assumed conviction that no such conversion ever does take place in the living frame. There is probably not more than a single known instance of the conversion of one organized principle into another out of the body. It is that of fibrin having become albumen under the ingenious proceeding of Denis. the reflections I have made on this subject incline me strongly to the belief that, so far as secreting organs are concerned, organized principles are inconvertible, and that in the function of assimilation, chiefly, if not alone, the great changes of elementary composition and organic constitution take place.

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There is certainly much similarity of constitution and origin in several of the substances we are now considering. It was once supposed that uric acid was the exclusive product of the carnivorous

tribe of animals, while hippuric acid was thrown off by the organs of the graminivora alone; but this appears to be a mistake, each acid being found in both classes of animals.1 Yet the old. opinion is so far correct, that uric acid abounds in the urine of the carnivora, with but slight traces of hippuric acid, while this relation is exactly reversed in the herbivora. This, indeed, might have been expected from the difference of food of these animals, hippuric acid containing a greater amount of carbon, and uric acid a larger proportion of nitrogen. This consideration again leads to the rejection of the idea that these substances are formed in the kidneys, and strengthens the conclusion, to which modern discovery points, that they are the products of the earlier processes of assimilation derived from the blood, and much influenced by the food and the organized structure of the secreting animal.

These facts may then, I think, be assumed to be established, that the three substances we are considering, viz., urea, uric acid, and hippuric acid, though derived from the food, are not imbibed with it, but are formed within the body, and enter the blood in the earlier stages of assimilation; that they are constant and necessary ingredients of that fluid; and that we are yet ignorant of any

1 Fownes, 'London and Edinburgh Philos. Mag.,' xxi, p. 139.

useful purposes they serve, and can only consider them in the light of refuse or effete matters, which, if not duly eliminated, are productive of much disturbance to health.

I have long had a strong conviction that, in the altered relation of these substances to each other would be found the explanation of many morbid phenomena. We have been too much in the habit of separating them in our minds, of viewing them as distinct and quite independent essences, instead of considering them as cognate and related things. Rejecting all consideration of hippuric acid, which chiefly concerns the lower animals, let us fix our attention on the two great secretions of man, urea and uric acid. When I say that they are related substances, I do not mean that, when once called into separate existence, they may, by any process of decomposition and recomposition, be made to pass into each other, but that, in certain morbid states of the system, the nascent urea becomes uric acid during the assimilation of the food. This opinion is at variance with the idea expressed by Liebig and Wöhler, who consider the uric acid as the parent of the urea; but I receive this opinion with great difficulty, because it implies the admission of the convertibility of organized principles, to which I have already pointed out the great objection; because urea is a voluminous and

constant product of health in all animals except birds and serpents, while uric acid seems to be wholly absent in some, and very scanty in most; and because the experiments related by Liebig and Wöhler, in which the uric acid is subjected to chemical decomposition, out of the body, urea being one of the results, do not in my mind warrant the conclusion that any analogous operation takes place in the living system. The passage in Liebig is the following:-" When uric acid is subjected to the action of oxygen, it is resolved into alloxan and urea; a new supply of oxygen acting on the alloxan, causes it to resolve itself either into oxalic acid and urea, or into oxaluric and parabanic acids, or into carbonic acid and urea." It cannot be denied that there is here cited the direct testimony of a fact. Urea has undoubtedly been obtained, by chemical processes, from uric acid; but urea has also been obtained by Wöhler through other chemical processes, in which no uric acid and, indeed, no animal organized principles were employed."

'Op. cit., p. 137, 2d edition.

? It would seem that this very plain expression of opinion might have saved me from misapprehension, but I find myself very unaccountably represented, in the work of Mr. Spencer Wells, as participating in the opinion of Liebig, that the lithic acid is the source of the urea, and that the "non-nitrogenized food, by monopolising a great proportion of oxygen to secure assimilation, and prevent development of lactic and acetic acid, prevents the conversion of lithic acid into urea, and the former remains in the blood in a greater or less proportion, and appears

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