upon the surface, and their fracture was somewhat foliated. It is also comparatively rare in its pure state, as an incrustation: I have seen it upon an uric nucleus, in a very large calculus, in the possession of Mr. Thomas.

The fusible calculus is always more friable than the triple; it is generally white, and often much resembles chalk in texture and appearance; it often breaks into layers, and exhibits a glittering appearance when broken, in consequence of the crystals of triple phosphate that have formed in its interstices.

The analysis of fusible calculus is perhaps best performed by distilled vinegar, which, when gently heated, dissolves the ammonio-magnesian phosphate, but not the phosphate of lime, which may be taken up by muriatic acid; and if any uric acid were present it remains as the ultimate residuum, and may be recognised by solubility in caustic potassa, &c. (page 67) Or the uric acid may, in the first instance, be separated by solution of caustic potassa, which also expels the ammonia, but has no action on the other ingredients of the calculus.

Calculi, or layers of calculi, composed entirely of phosphate of lime, were first described by Dr. Wollaston under the name of bone-earth calculi; their surface is generally pale brown, smooth, and, when sawed through, they are found of a laminated texture, and separate easily into concentric crusts. Dr. Wollaston also notices an appearance which I have often remarked, that of each lamina being striated in a direction perpendicular to the surface, as from an assemblage of crystalline fibres. This calculus is of very difficult fusion. It is soluble in muriatic acid, and ammonia precipitates phosphate of lime from this solution.

The aspect and chemical characters of the uric calculus have already been adverted to. Their texture when formed in the bladder is generally laminated; and when cut into halves, a distinct nucleus of uric acid is almost always perceptible. Their exterior is generally smoother than that of other calculi, excepting those of phosphate of lime.

It rarely, and perhaps never, happens, that a bladder calculus consists of any of the above substances perfectly pure. Traces of the phosphates are discoverable in the uric calculus, and of uric acid in those composed of the phosphates, and the mode of analysis has already been pointed out.

It is, however, a common circumstance to find two or more of the above substances in layers distinct from each other. Uric calculi incrusted with the phosphates are of very frequent occurrence; they are indeed the most common of all calculi. Sometimes the nucleus only is uric, the bulk of the calculus being of the phosphates; at other times a comparatively large uric calculus is incrusted with a thin coat of the phosphates; but I have never yet seen a bladder calculus with a well defined nucleus of the phosphates enveloped in uric acid.

Besides the calculi composed of uric acid and of the phosphates, two other substances have been mentioned as belonging to this formation, oxalate of lime, and cystic oxide.

The properties of oxalate of lime have been described in speaking of it as of kidney origin, but its appearance when concreting into calculi in the bladder is peculiar; their exterior is rough and tuberculated, and their colour deep reddish brown, so that they have been termed mulberry calculi. Dr. Marcet (Essay, p. 78,) has described a variety of the oxalate of lime calculus not exceeding the size of a pea, of a pale brown colour and crystalline texture, of which he has seen three specimens. The superficial crystals were very flat octoedrons.

The nuclei of these calculi are generally oxalic, and of renal origin, but uric nuclei enveloped in the oxalate also occur; they are likewise not very unfrequently found enveloped by the fusible calculus. I have in my possession a calculus of which the nucleus is uric, surrounded by oxalate and phosphate of lime, and triple phosphate, each in a distinct layer; and Dr. Marcet has depicted a very analogous specimen. (Essay, Plate VIII., fig. 8.)

The cystic calculus is rare compared with the other varieties. In appearance it most resembles the triple phosphate, but it is

somewhat tough when cut, and has a peculiar greasy lustre. It is usually of a pale fawn colour bordering upon straw yellow, and of an irregularly crystalline texture".

The calculi which have now been described may all be considered as of renal origin, that is, as formed upon nuclei that have passed from the kidneys into the bladder, where they have lodged and increased in bulk, that increase depending at times upon a morbid state of urine, and at times being the simple consequences of an extraneous substance lodged in the urinary passages; in the former case it is uric acid, or oxalate of lime, or cystic oxide; and in the latter, generally speaking, phosphate of lime, or ammonio-magnesian phosphate, or the mixed fusible phosphate

Independent, however, of the ordinary disposition of the urine in its healthy state to deposit the phosphates upon any extraneous matter in the passages, it often acquires a greatly increased tendency to do so in consequence of general disease or local injury. There are, as has already been stated, particular states of stomach and bowels, or of the general health, that favour the formation of the phosphates; local injury of the spine produces an alcaline urine; and when, from any cause, such as stricture, or diseased prostate gland, or calculus, the bladder does not quite empty itself, the remaining portion of urine is

* Dr. Marcet, in his Essay on Calculi, has mentioned two nondescript substances forming concretions in the bladder. One of these he has termed Xanthic oxide, from the yellow-coloured compound which it produces when acted on by nitric acid; it is more soluble in water than uric acid, and is distinguished from cystic oxide by its inferior solubility in acids. The other is called a Fibrinous Calculus, and appeared to consist of hardened albuminous matter.

I once met with a calculus having a nucleus of albuminous matter, probably analogous to that described by Dr. Marcet; the specimen I gave to Mr. Wilson, and is, I believe, preserved in the Museum in Windmill. street. I attributed the origin of this stone to a clot of blood having been retained in the bladder during the voiding of a large quantity of uric gravel, which had produced copious hæmorrhage; but I do not think that calculi can often result from such a cause, in consequence of the facility with which any coagula of blood are generally softened and voided.

very apt to undergo a slight decomposition, in which case it becomes ammoniacal, and more or less of the phosphates will of course be thrown down. This accounts for the circumstance of those calculi which have attained a very large size in the bladder, consisting chiefly of the phosphates; and shews why a similar deposition is often formed upon bougies, or any other extraneous body; why uric nuclei are so often incrusted by phosphates; and why in some cases of diseased kidney a similar deposition has often gone to a great extent.

An enlargement of the prostate gland is not only favourable to the increase of the size of a calculus for the reason which has just been adverted to, but in some instances becomes the cause of the formation of a stone, quite independent of any mischief in the kidneys, or disordered secretion of urine." The bladder never being completely emptied, the dregs of the urine, if I may be allowed the expression, being never evacuated, a calculus, formed on a nucleus of the ammoniaco-magnesian phosphate and mucus is produced, when it would not have been produced under other circumstances. This species of stone, or a stone upon such a nucleus, can only be produced where the bladder is unable to empty itself; it may therefore be arranged among the consequences of the enlargement of the middle lobe of the prostate gland." (Home on the Diseases of the Prostate Gland, Vol. I. p. 40.)

Another way in which any obstacle to the emptying of the bladder becomes a source of mischief in calculous cases, is that under such circumstances, the quantity of urine secreted during a given time is diminished, only eight or ten ounces being in some instances voided during the 24 hours. An illustrative case of this kind will be found in Sir Everard Home's treatise just quoted, (p. 44.) and it always happens that the specific gravity of such urine is greatly above the natural standard, and that it becomes very turbid on cooling, even when voided clear, which, however, seldom happens.

Having now, I believe, enumerated the leading circumstances respecting the composition and formation of calculi of the urinary bladder, it remains to make a few observations upon the

symptoms that are peculiar to them, and upon the different methods of treatment which they require.

It is not necessary here to enter into the ordinary symptoms of calculus of the bladder, which are so well known, and have been so frequently described; nor shall I, for obvious reasons, notice the uncertainty and difficulty that frequently attends ascertaining the situation and size, and often the existence even of a calculus, by the operation of sounding. The general state of the urine, and of the matters voided with it, are the principal circumstances that bear upon the medico-chemical treatment of this disease; and the passing of different kinds of sand, and of mucus, together with the composition of the urine relatively to its healthy state, are the circumstances to which we must look as those symptoms of the nature and progress of the malady which are chiefly to guide us in its treatment.

Considered in this view, the treatment of calculus was usually pursued upon very erroneous and generally, merely upon empirical principles, until Dr. Wollaston pointed out those differences in the composition of calculi, which I have described, and which were first made known by the publication of his essay in the Philosophical Transactions for 1797. Previous to that period it was customary to consider all calculi as of one kind, and soluble in caustic alkalis; these, therefore, became the prevalent remedies, and have continued so even till now, under the absurd name of solvents; even at present it unfortunately happens that but little of the information contained in that paper is known to, or understood by those to whom the treatment of the cases in question is usually trusted; perhaps for want of explicit directions as to the manner in which the discoveries alluded to were to be brought to bear upon practice; this was one of the main ends of those papers which the Royal Society has done me the honour to publish in their Transactions, (Phil. Trans. 1808, &c.) and the deficiency has since been made good in a more able and connected manner by the publication of Dr. Marcet's essay.

When a stone has once lodged in the bladder, and increased there to such a size as no longer to be capable of passing the urethra, it is, I believe, generally allowed by all those who have