any unusual length of time. This will not so much occur when absolute retention takes place, as when from any cause the bladder is never emptied entirely of its contents. This causes irritation of the mucous membrane, and an increased discharge of mucus, which, being retained also, is present in unusual quantity. Whether by means of the mucus, or on its own account, we do not pause to discuss-but urea is decomposed, making the urine ammoniacal. A small part of this ammoniacal urine is always retained, and induces quickly an analogous decomposition in the fresh arrivals from the ureters. The urine is then discharged alkaline, thick, and fetid. But when the bladder is thoroughly emptied and washed out by injection, an acid urine will immediately collect in it.

This is the physiological explanation of these cases, as proved by experience, reason, and experiment. Let the retention be due to paralysis of the bladder, from whatever cause, affection of any part of the spine, from hemiplegia or paraplegia, or from difficult childbirth; let it be due to the presence of diverticles of the bladder, to calculi or foreign bodies, to enlarged prostate, to stricture of the urethra ; or let the retention be caused by the perverse will of insanity, in which excretions are frequently held back, entirely or in part; or let partial retention occur in the coma of fever-it will always have the same effect, decomposition of urea and ammoniacal urine.

There are some rare and extraordinary cases, in which phosphate of lime is said to continue to be discharged in the urine for a long time without apparently doing much mischief. Such a case is recorded by Dr. G. Bird (p. 291). The patient was an old man, an habitual dyspeptic, and had laboured under pyrosis from boyhood. He had during many years been in the habit of passing almost milky urine, which on repose deposited such an extraordinary quantity of phosphate of lime, that he brought to Dr. G. Bird, at one time, more than an ounce of the salt. He had during the last fifty years been under the treatment of half the hospital physicians and surgeons in London. At the same time this man's general health was so good, that there was scarcely an excuse for submitting him to any course of treatment, beyond the apprehension of the possible formation of a calculus. This man was most probably an impostor. No pretence could lead him to the hospital, from which during a fifty years' experience he had derived no benefit regarding a symptom, which, if really present, left his health intact. To collect an ounce of the earthy phosphates must have engaged him for sixteen days, supposing it all to be derived from his own.

excretions. And no man will take that trouble knowingly for no purpose; his object must be to make himself interesting in the eyes of the physician, and, if possible, to derive the benefit of being kept in the charity some time.

If the reader should not share our doubts, he may adopt the explanation by Dr. G. Bird, for which, however, there is no basis in fact; or he may explain it upon the ground of the following observation recorded by Dr. Prout (p. 323, note). This physician examined the body of a gentleman who, during the greater part of his life, had suffered from renal disease, remarkable for being attended by the secretion of large quantities of the earthy phosphates. Both kidneys were not only extensively disorganized, but most of the natural cavities, as well as many cysts, were found distended with numerous carthy concretions, of various sizes and composition. The concretions found in those cavities to which the urine had access, consisted of the phosphate and carbonate of lime, and more or less of the triple phosphate of ammonia and magnesia, while those cavities or cysts distinct from the renal structure, and to which, therefore, the urine had no access, consisted of the calcareous phosphate and carbonate only, without any admixture of the triple phosphate.

From a consideration of many cases of earthy calculi, it is apparent that the mere presence in the bladder of deposits of the earthy phosphates never gives rise to calculi. For such a concretion to form, it requires the presence of some binding material, such as ropy mucus, or a clot of blood, or fibrine. It is for this reason that urine, which deposits the earths in the bladder under the influence of fixed alkali, has never been known to form a calculus. It is only with the aid of hæmaturia, or chronic disease of the mucous membrane, that calculi are formed. In accordance with this, calculi are rare in the bladder of herbivora, which discharge alkaline urine, and therefore always mixed with a large proportion of a deposit of earthy phosphates.

Carbonate of lime is met with in some urinary concretions, but very rarely. The above observation of Dr. Prout illustrates the circumstances under which it may occur. It is a regular ingredient of the urine of herbivora. I have examined prostatic concretions consisting nearly entirely of this substance. But it is always questionable whether the lime or carbonic acid were in any case derived from the urine.

CHAPTER XIV.

IRON.

Symbol: Fe. Equiv.: 280.

I am obliged to treat of iron in this place, though it would perhaps have been more properly arranged under Uræmatine, of which substance Dr. Harley has shown that it always forms an integral part, thus indicating its derivation from hæmatine proper. In the course of time we may perhaps succeed in finding the proportion in which iron is contained in uræmatine; and in that case this metal would be valuable for determining the quantities of this colouring principle in the urine.

Besides the iron normally combined with uramatine, an accidental quantity may be present in the urine, after the ingestion into the system of preparations of iron. These latter combinations yield the ordinary tests for iron with the usual reagents, and therefore differ considerably from the iron combined with uramatine, which is not influenced by the addition to the urine of the usual test-solution for iron. For the iron of uramatine to exhibit its ordinary properties, it requires the total destruction, by heat, of the organic substance with which it is combined, and, after solution in a mineral acid, it becomes accessible to the tests.

Chemical properties.

When to the solution in hydrochloric acid of the ashes of urine a drop of nitric acid is added, and afterwards sulphocyanide of potassium, a reddish colour is produced by the presence of the smallest traces of iron, and a deep red by the presence of larger quantities.

Another portion of the solution of the ashes, after boiling with a little nitric acid and dilution with water, may be treated with ferrocyanide of potassium, when immediately a

precipitate of Prussian blue will ensue, if the quantity of iron present be large. If, however, traces only are present, it will require several hours' standing for the blue flakes or light clouds of Prussian blue to become visible by deposition.

Marguerite's method of determining the quantity of Iron in Urine.

When a solution of suboxyde of iron in an excess of hydrochloric acid, is mixed with a solution of permanganate of potash, the suboxyde is transformed into oxyde, and the permanganate reduced to manganate. One equivalent of permanganate of the composition Mn,O,+KO yields 5 equivalents of oxygen, and thereby transforms 10 equivalents of suboxyde of iron into oxyde. A solution of permanganate of potash of known strength, therefore, may serve to determine the quantity of iron contained in any solution in the form of suboxyde, if added in a quantity just sufficient to effect the oxydation. This quantity may be accurately determined by the loss of colour which the permanganate undergoes as long as it is continued to be reduced; but a single drop of this fluid which is added, over the quantity necessary for effecting the transformation into oxyde of the whole of the suboxyde present, imparts to the mixture a light-red colour, which indicates the completion of the analysis.

Preparation of the standard solution of permanganate of potash. We dissolve crystallized permanganate of potash in an ad libitum quantity of water, and determine the strength of a given volume of this solution by the following standard solution of ferrocyanide of potassium, given by Neubauer :7513 grammes of pure, crystallized, dry ferrocyanide of potassium, containing 10 gramme of iron, are dissolved in so much water, that the solution exactly amounts to one litre. 10 c.c. of this solution contain exactly 10 milligrammes of iron. 10 equivalents of ferrocyanide of potassium require 1 equivalent of permanganic acid to be transformed into 5 equivalents of ferricyanide of potassium.

Of this solution we now take 100 c.c., containing 10 milligrammes of iron, dilute it with about 50 c.c. of water, acidulate with hydrochloric acid, and after having placed the beaker upon a piece of white paper, we add the solution of permanganate of potash to the solution of iron, which latter is kept in a rotating motion. The appearance of a yellowish-red colour indicates the completion of the test. Supposing the 10 milligrammes of iron contained in the 10 c.c. of solution of the ferrocyanide required 20 c.c. of the solution of per

manganate of potash for complete oxydation, 1 c.c. of the 05 milligramme

latter fluid would correspond to

0.010
20

of iron. The strength of the solution of the permanganate of potash may also be determined by the solution of chloride of iron of known strength described under phosphoric acid, or by the solution of oxalic acid of known strength, described under the analysis for phosphate of lime. By calculation of the equivalent, it may easily be adapted to the equivalent of

iron.

Application to the urine.-The ashes of a given bulk of urine, say 100 c.c., burned perfectly white, if necessary, by the aid of nitrate of ammonia, are dissolved in hydrochloric acid. The chloride of iron has now to be reduced to the state of subchloride. This is best done by dissolving pure zinc, which has been expressly ascertained to be free of iron, in the acid solution, until the latter has lost all its colour (method of Schwarz'). It is now freed from the excess of zinc and other matters by filtration, and diluted to the bulk of about 50 c.c. The solution of permanganate of potash of known strength, as determined before use, is now added to the solution of iron, and mixed with it by agitation until the red test appears. Supposing 1 c.c. of the solution of permanganate of potash to be graduated for 0.0005 grammes of iron, and supposing that we have used for the oxydation of the suboxyde of iron obtained from 100 c.c. of urine, 3 c.c. of the standard solution of the permanganate, they would indicate 3 x 0.0005 grammes 0.0015 grammes of iron. Supposing that of this urine 15000 c.c. were discharged during twenty-four hours, the amount of iron thus secreted would be 0.0225 grammes.

The disappearance of the red colour test after standing a little while, is due to further changes not in connection with the analysis, and need not, therefore, be regarded by the experimenter.

Physiology and Pathological indications of Iron.

We know that iron is a component part of the red colouring matter of the blood or hæmatine, and that a deficiency of iron in this substance, or in the blood and organism generally, constitutes a feature of certain diseases, which generally pass under the name of chlorosis and anæmia. The similarity to hæmatine which uræ matine exhibits, by its con

1 Maassanalysen,' p. 120.