892 16 20 2 COLOURING MATTERS OF THE BILE. Stædeler gives its formula more than bilirubin. The character; it is insoluble in the green colouring matter of vegetables, an opinion since found to be erroneous; Stædeler's analysis leads to the formula (€16H20N25). It is insoluble in water, but is taken up by alcohol and by ether. The cholepyrrhin, or biliphæin, obtained by Brücke crystallized from its solution in chloroform, according to Maly, is an amide of biliverdin. In human bile the brown pigment preponderates; it has been termed bilifuscin. This bilifuscin is soluble in absolute alcohol, but insoluble in chloroform and in absolute ether, and nearly insoluble in water. as €18H0N, or as containing H, red colouring matter is of an acid water, sparingly soluble in alcohol and in ether, but soluble in chloroform, from which it may be obtained in crystals of a dark red colour (EH,N,,; Stædeler), and is by this chemist called bilirubin. It combines with the alkalies, forming solutions which are of a deep orange-yellow, and when largely diluted, of a yellow colour, like that of a jaundiced person; with the earths it forms compounds which are insoluble in water and in alcohol. This brownishred colouring matter of the bile is very rapidly altered by reagents. The changes of colour produced in it by the action of nitric acid. have been proposed as one means of detecting the presence of bile in certain cases, as, for instance, when it occurs in urine: when a solution containing this colouring matter is mixed with nitric acid, the colour becomes at first green, then blue, passing rapidly into violet; it then changes to red, and finally the red passes slowly into yellow. 16 181 2 Many biliary calculi contain a large quantity of the colouring material in combination with lime, with which it forms a brown compound insoluble in water. Calculi are also frequently found in the ox composed of a pure intense yellow colouring substance, much prized by artists for its durability and for the brilliancy of its tint. The greater part of the colouring matter of the bile, with a small portion of bile itself, passes off with the fæces, but by far the larger proportion of this secretion is reabsorbed into the system, where it has been conjectured to supply a portion of the material consumed by the oxygen in respiration for the maintenance of animal heat. This theory, however, seems to be questionable, since the constituents of the bile have not been satisfactorily discovered in normal blood. The resinous acids of the bile, which constitute the characteristic components of this secretion, appear to be truly formed by the liver itself. The mode of action of the liver differs there EXCREMENTITIOUS PRODUCTS—THE URINE. 893 fore in an important manner from that of the kidneys, since these glands do not produce the compounds excreted by them. (1704) Sugar is not an ingredient in normal bile, but it is remarkable that this substance is formed rapidly from one of the constituents of the liver itself, in which organ sugar is found in considerable quantity after death (Bernard). The full significance of this fact, in its physiological bearings, cannot be said to be at present understood. In cases of metallic poisoning, the liver has generally been found to contain traces of the metal that has been exhibited, but it is important to bear in mind that iron, copper, and manganese are always present in minute quantity in the ashes of healthy human bile. Lead, arsenic, and antimony have been detected in the liver, in cases where they had been taken in poisonous doses; and there is no reason to suppose that traces of these substances would not be found in the liver, if duly sought for after death during the exhibition of these metals in medicinal doses. C. Excrementitious Products. (1705) 1. THE URINE.-This fluid is separated by the kidneys from arterial blood. Human urine, to which the following remarks are applicable, unless otherwise specified, is usually of a light amber colour, and, if passed when fasting, is feebly acid to litmus; but, according to Bence Jones, the acidity diminishes during digestion, and whilst this process is most active, the urine is often found to be slightly alkaline. Urine has a peculiar odour, and a saline bitter taste. Its specific gravity varies with the diet and state of health of the individual, but it usually averages about 1020. The quantity passed during the twenty-four hours also varies with the quantity of liquids taken, but on an average it may be estimated in the adult at from 40 to 50 ounces. Urine, when left to itself, speedily begins to undergo change. In most cases it first exhibits an increase of acidity, as Scherer has shown; but after standing for a few days it begins to putrefy, and then acquires a powerfully alkaline reaction and an ammoniacal odour, owing to the conversion of the urea into ammonium carbonate. This alkaline decomposition of the urine sometimes takes place within the bladder, particularly after injuries to the spinal cord attended with paralysis of the lower part of the body. The mucus of the bladder appears to act as a ferment upon the urine, and has a large share in producing this decomposition of the urea. Composition.-Urine contains among its components, urea, a 894 COMPOSITION OF URINE. small quantity of kreatine and kreatinine, uric acid, traces of hippuric acid, and hydrochloric, sulphuric, and phosphoric acids, in combination with potassium, sodium, calcium, magnesium, and traces of ammonium. It also always contains a little vesical mucus, together with some other ill-defined azotised principles. In addition to these bodies, Stædeler has noticed the presence of minute quantities of certain acids homologous with the carbolic and with oleic acid. The bodies contained in the urine are mainly the products of oxidation, occasioned by the action of respired air upon the nitrogenised tissues, and upon the sulphur and phosphorus which they contain. The following table represents the composition of an average sample of healthy human urine : The quantities of the various components of the urine are, however, subject to material variation, even in the same individual at different times, although he may be in perfect health. The quantity of solid matters, and especially of urea, is proportionately somewhat increased with the increased amount of exercise taken, as the direct experiments of Lehmann have shown. Indeed, it has been found to be a general rule that the waste and reparation of the body are in direct proportion to the amount of exercise taken during active exercise the number of inspirations in a given space of time is increased, a larger quantity of oxygen is brought into contact with the blood and the tissues, and a more rapid waste of their components ensues, and consequently a greater URINE IN DIFFERENT CLASSES OF ANIMALS. 895 supply of food is demanded after exercise than after the individual has been in a state of repose for an equal interval. In all animals the urine appears to form the principal outlet. for the nitrogen of the effete azotised tissues of the system, though the compounds in which it is excreted vary with the kind of animal.* Carnivorous animals, such as the lion, the tiger, and the leopard, excrete the greater part of the nitrogen in the form of urea; and produce but a small quantity of uric acid. The urine of these animals is clear, and nearly colourless, with a strongly acid reaction; but it putrefies rapidly, and quickly becomes alkaline, owing to the decomposition of the urea. The herbivora likewise excrete a large quantity of urea; but hippuric acid in considerable quantity is contained in their urine, whilst uric acid is nearly wanting. Many of these animals, such as the rhinoceros and elephant, excrete a urine containing a large quantity of the bicarbonates of calcium and magnesium, in consequence of which their urine is either turbid when voided, or it speedily becomes so. The phosphates are almost entirely absent from the urine of the herbivora, but they occur abundantly in the fæces of these animals. Carnivorous birds excrete uric acid in abundance in the form of a superurate of ammonium, and they also appear to excrete small quantities of urea : but urea is completely absent in granivorous birds, which excrete abundance of uric acid combined with a variable amount of ammonia. In those carnivorous reptiles which live out of water, such as the serpent tribe, the excretions consist almost entirely of uric acid; while in the amphibia, such as the frog and the toad, urea appears, with very little uric acid. Uric acid has also been found in the excrements of insects. From these facts, it is clear that in those animals which drink freely, the nitrogen is excreted principally in the form of urea, while in those which take very little fluid nutriment it is separated chiefly in the form of uric acid. In diseases attended with fever the quantity of uric acid in human urine is greatly increased. The question of the source whence uric acid is derived is full of interest, especially to the practical physician, since its morbid prevalence is intimately connected with some of the most distressing maladies which afflict the human frame, such, for example, as gout, rheumatism, and certain forms of calculous concretions from the urine. In some * Ranke estimates the quantity of nitrogen which passes off by the alvine evacuations in man at of that excreted by the kidneys, but nearly the whole of this is derived from undigested portions of the food; it must vary with the nature of the food, and but a very small proportion, if any, has any connection with the waste of the tissues. 896 URINE-PROPORTIONS OF UREA AND URIC ACID. kinds of gout, uric acid is developed and retained in the system, chiefly in the form of sodic urate, in the neighbourhood of the smaller joints, such as those of the fingers and toes and the wrists, forming deposits commonly known as chalk-stones. The system is in these cases loaded with lactic and acetic acids, the latter of which is thrown off abundantly in acid sweatings. Dr. Garrod, in cases of gout, has invariably found uric acid to be present in the blood, and he has also frequently detected it in the blood in Bright's disease: it has been found occasionally in healthy blood. Uric acid is likewise discovered without difficulty in the blood of animals from which the kidneys have been extirpated. The composition of the urine is found to vary at different times of the day. That voided in the morning, for example, after the lapse of a considerable interval without the ingestion of food, is the result chiefly of chemical actions going on within the body itself, and is furnished by the decomposition of the tissues. Such urine has a very different composition from that passed in the evening, into which various bodies have been absorbed directly from the stomach. These bodies necessarily vary with the food, and variation in the quality of the food is also the principal cause of variation in the quantity both of uric acid and of urea. In proportion to the quantity of nitrogen contained in the food, the proportion of urea excreted increases. This was distinctly proved by C. G. Lehmann, and his results have been confirmed by all subsequent observers. With reference to this point, it was found by Lehmann in a series of experiments upon his own person, that after restricting himself to an animal diet for twelve days, he excreted daily 821 grains (532 grms.) of urea, and 216 grains, or 14 grms. of uric acid. After an exclusively vegetable diet for a similar period, the quantity of urea in twenty-four hours amounted to 348 grains, or 225 grammes, and the uric acid to 15'4 grains, or 1 grm.; and after subjecting himself for three days to a diet from which nitrogen was as far as possible excluded, the quantity of urea fell to 237 grains (154 grms.). When a highly azotised diet was taken, the same observer found that five-sixths of the entire quantity of nitrogen taken in the food were eliminated from the system in the form of urea. With an ordinary mixed diet, according to observations extended over 15 days, the urine amounted to 37'3 ounces daily, and it contained 501 grains (325 grms.) of urea, and 18.2 grs. or 1183 grms. of uric acid. This quantity of urea thus obtained during the use of an ordinary mixed diet agrees very closely with the average results collected |