admirably arranged to receive the albumen reabsorbed by the epithelium; and so, too, are the capillaries of the malpighian tufts (the glomeruli) arranged to allow a filtration of the serum; in fact, it is owing to this circulatory system, which we have called the renal portal vein, that the solution of this twofold phenomenon may be found, viz. filtration and reabsorption, which constitute the two phases essential to the secretion of urine. Comparative physiology illustrates this twofold phenomenon still more perfectly: among the ophidians (snakes, etc.), which secrete a solid urine, a liquid is found at the beginning of the uriniferous tubes, which gradually becomes thickened in its course, until it finally acquires the characteristic semi-solid consistency.

Thus, to sum up, the secretion of urine is composed of two distinct phases: 1, A phenomenon of simple filtration in the glomerulus; 2, To this purely mechanical phenomenon there succeeds a vital work on the part of the globular elements of the epithelium of the uriniferous tubes.

This epithelium of the uriniferous tubes, then, simply absorbs, but does not secrete; formerly it was supposed to have something to do with the formation of urea, but it is now proved that all the urea found in the urine is primarily contained in the blood. The origin of urea in the kidney is reduced to a simple question of experiments, the results of which show that urea pre-exists in the blood, and is not formed in the kidney; that the blood of the renal vein normally contains less urea than that in the renal artery; that ligation of the ureters produces the sume symptoms as ablation of the kidneys. In France, Prévost and Dumas, Ségalas and Vauquelin,1 Cl. Bernard and Barreswil, Picard 2 (Thèse de Strasbourg, 1856), have arrived at these results; yet, in Germany, their researches have been opposed on account of an assumed error in the estimation of urea; Oppler, Perls, Hermann, Hoppe-Seyler, and Zalesky contend that a large amount of urea is formed in the renal tissue, just as ptyaline is formed in the salivary glands; a maceration of kidney gives origin to urea in the same way that a maceration of the parotid gland gives rise to animal diastase. Finally, Zalesky pretends that ablation of the kidneys (nephrotomy) and ligation of the ureter produce different symptoms; that, after

1 Journal de Magendie. Vol. II. p. 354.

2 J. Picard," De la Présence de l'Urine dans le Sang et de sa Diffusion dans l'Organisme."

ligature of the ureter, urea is found in much greater abundance in the blood, and more rapidly induces uræmic poisoning. This question has been decided by the employment of an incontestable means of estimating the amount of urea, viz. by the process employed by Gréhant: with Millon's reagent, or the nitrous-nitrate of mercury, the urea is decomposed into equal volumes of carbonic acid and nitrogen; the especial precision and characteristic feature of this process depends upon the collection of all the carbonic acid and all the nitrogen, that is produced by this reaction, in such a manner that in each analysis the equality of the determined volumes of carbonic acid and nitrogen will render certain that only urea has been decomposed. In this way it has been demonstrated, that the accumulation of urea, after the operation of nephrotomy, occurs in a continuous manner; and that in this case, as after ligation of the ureters, the quantity of urea which accumulates in the blood is equal to the amount that the kidneys would excrete; that after ligation of the ureters, the blood which leaves the kidney contains exactly the same amount as that which enters this organ; that in the normal condition of the blood the renal vein contains less urea than the renal artery, and that this deficit precisely corresponds with the quantity of urea which is thrown off by the urine1 during the same period of time. We have then the right to conclude in an incontestable manner, that the kidney is simply a filter, in which urea is eliminated, that is, the renal filter can be impregnated with this substance and give it up by drainage.

B. Composition of urine.

Urine is secreted during 24 hours in variable quantity, in the normal condition to the amount of 500 to 1500 grammes. This urine is an aqueous solution of various principles: its elements in solution are pretty constant in quantity, the variation being due to the proportion of water; in fact, the urine is more or less abundant during health, because it may be more or less diluted.

The quantity of water in the urine depends upon the conditions of the circulation and blood; as the urinary secretion is a filtration resulting from pressure, when the arterial

See Gréhant," Cours de l'Ecole Pratique de la Faculté de Médecine de Paris." ("Revue des Cours Scientifiques." Nov.,

tension increases, more urine, or, correctly speaking, more water will be excreted; so also when the arterial tension is diminished, the urine will be less abundant. Physicians know full well that there is no necessity for prescribing diuretic medicines for patients whose pulse is very soft and feeble, and that in such cases the best diuretic will be a drug that will stimulate the force of the heart and the circulation. With this understanding the urinary secretion is very important, for it forms a sort of safety-valve by means of which the blood is freed of an excess of water. After a meal there is a sort of general plethora, an augmentation of the blood tension, and consequently an abundant and diluted urine will flow (urina potûs et cibi). In the morning, however, the urine secreted during a previous night of repose is more concentrated and scanty, because there has been no cause to increase the quantity of liquid in the blood nor its pressure. The lungs eliminate a slight amount of water. A proportion between the weight of the organism and the quantity of solid residue contained in the daily urine may be calculated. Each kilogramme of the weight of the animal is represented by one gramme of anhydrous urine. Yet this proportion may vary according to the season or character of food.

A man weighing 65 kilos. will excrete, on an average, 65 grms. of anhydrous urine. Nearly one-half (30 grms.) of the anhydrous daily urine is represented by a substance, urea, that we have mentioned before when speaking of all of the other liquids of the organism. This substance is a nitrogenous principle. More nitrogen is eliminated in urea than in any other excrementitial product. It has been demonstrated that the urea excreted is almost all (according to Lehmann, four-fifths) that which can be produced from the food we eat; the remaining one-fifth may be accounted for when we recollect that the respiratory excretion, as well as the epidermal exfoliation and the secretion of sweat, contain a small amount of urea. There is also found in the urea about one-fifth of the carbon, which must be added to the 500 grms., that we daily excrete by means of the lungs.

The amount of urea may vary under the influence of certain well-defined conditions; since it is the residue from the combustion of albuminoids in the organism, its abundance will depend upon the amount of animal food contained in nutriment.

In a general way it may be stated that there is a direct

ratio between the degree of animal heat and the amount of urea eliminated (Hepp and Hirtz).1

The remaining 35 grms. of anhydrous urine (half the amount eliminated in a day) is distributed as follows:

There are 15 grms. of matters called extractive, that is, products of incomplete combustion of the albuminoids: to this class belong creatine, creatinine, etc., but the most interesting of this class is uric acid, not found in large quantity, it is true; but which, under certain circumstances, can be accumulated to a large extent, or be retained in the tissues (uric acid diasthesis; gout; tophus of urate of soda). In the normal state this substance exists in proportion to the urea, as 1 is to 30; that is to say, that 1 grm. is found in the urine of 24 hours. Its especial characteristic consists in its sparing solubility in water, which dissolves only go of its weight. On account of its difficult solubility we cannot explain how uric acid exists in solution in the urine; it may be in combination with soda as urate of soda; yet, as this latter is scarcely any more soluble than uric acid (150), we must suppose that uric acid or the urates are dissolved by the aid of the acid phosphate of soda (that which gives to urine its acid reaction), or by that of the coloring matter. It is known that if urine be allowed to stand while exposed to the air, a species of lactic acid fermentation ensues, by which a large portion of the coloring matter seems to be destroyed and uric acid to be formed. Among many of the herbivora an analogous acid, hippuric acid, apparently replaces the uric acid; this former acid is composed of benzoic and glycocholic acid: in fact, man can make this acid appear in his urine by the ingestion of benzoic acid; glycochol or sugar of gelatine is by this means provided by the metamorphosis of the connective tissue.

There now remain but 20 grms. of anhydrous urine for whose composition we must account; these 20 grammes are represented by the salts, of which chloride of sodium forms 8 parts, and various other salts 12 parts (sulphates, phosphates, lactates, &c.). The base of these salts is mostly soda; there are also some salts of lime held in solution by means of an excess of acid. Alkaline urine, as from the herbivora, for instance, is turbid; and horse-urine is employed as a type

See Art." Fièvre," in Vol. XVI. of the "Nouveau Dict. de Médecine et de Chirurgie Pratiques."

for the designation of urine which is turbid or alkaline owing to some pathological cause, hence called jumentous urine. The phosphates are usually made up of the alkaline earthy salts, there being in the urine passed during 24 hours about one or two grms. of phosphate of lime and magnesia. It is worthy of note that the kind of alimentation has a certain influence upon the presence of the phosphates and sulphates in the urine; we usually take but a small quantity of sulphur and phosphorus as contained in the organic products (albumen, proteine, gluten, etc.). When the proteine substances are burnt up in the organism and transformed into urea, they cause an oxidation of the sulphur and phosphorus, and form sulphuric and phosphoric acid. This explains the fact that the phosphates and sulphates simultaneously vary in quantity in the urine, according to the same laws as urea. We have already learned that a certain amount of sulphur (nearly 4 grms. in 24 hours) is found in the bile as tauro-cholic acid.

The pretended Kiesteïne (more properly Kyesteïne), noticed by Nauche and Golding-Bird, occurring in the form of a peculiar albuminoid pellicle floating on the urine of a preg nant woman does not constitute a definite compound. This is composed of an ammoniaco-magnesia phosphate and of a substance not yet precisely determined, called gravidine (a particular albuminoid compound) by J. Starck, a caseine substance (the elements of the commencing secretion of milk which passes by reabsorption into the blood and thence into the urine) by G. Bird, mucus and a proteine substance by Lehmann, infusoria and vibriones by Béchamp, etc.

There is nothing precisely known of the influence of the nervous system upon the urinary secretion. From what precedes it is probable that this influence is reduced to a vasomotor action, which modifies the afflux and presence of the blood in the capillaries of the glomeruli and renal tissue.

M. Peyrani has sought, by means of numerous researches on animals, to explain the part played by the great sympa thetic on the urinary secretion. He determined the amount of urine and urea first secreted during the six hours preceding experimentation, then the six hours during the galvanic irritation of the sympathetic, and again during the six hours succeeding the section of the sympathetic; and observed that this quantity was greatest in those cases where the sympathetic had been cut (a section of the cervical portion of the sympathetic was made), while galvanization of the distal end of the divided sympathetic brought the quantity