phosphat of lime calculus, and its ammoniacal portions will be come disengaged by the heat of a blow-pipe, leaving the remaining phosphate of magnesia opaque, and susceptible of an imperfect fusion. The fusible calculus is easily distinguished when subjected to the flame of a blow-pipe, by melting, bubbling up, and running into globules of a pearly appearance. This also is readily dissolved by acids, and especially by the diluted muriatic acid. The mulberry calculus is, as already stated, for the most part sufficiently easy of detection, by its external characters. Its most obvious chemical character is, to swell out, when exposed to heat, and to expand into a kind of white efflorescence, which, when brought into contact with paper, stained with the juice of violets, and slightly moistened, turns it green.' This calculus does not indicate much solubility by trial with either the acids or alkalies. The cystic calculus is distinguishable by its peculiar waxy appearance, and by its peculiar smell when heated. This concretion soon yields both to acids and to alkalies.

Such, then, are the concretions most commonly observed in or about the urinary organs, and such the mode in which their. several constituent principles may be best developed. There are one or two others noticed by Dr. Marcet, of a sui generis kind, but which are so unfrequent in their occurrence as to be scarcely worthy of notice. We shall therefore proceed to advert briefly to the quo modo of their generation. The more commonly received notion respecting calculous formations, is, that they are precipitates from the urinary secretion, in consequence of one or other of the several ingredients of which urine is formed, either becoming disproportionately increased, or inordinately diminished, and thus forming insoluble compounds, which are precipitated and retained instead of being discharged, The late Dr. Austin, however, in a very ingenious treatise on Stone, published in the year 1791, contends for a different theory of calculary concretion. This writer conceives, that the proximate cause of the disease, or stone, does not exist in the uriniferous vessels of the kidney, or in the fluid secreted from them, but in the coats and glands of the several cavities through which the urine passes. In support of this principle, he alleges, that mucus readily forms stone out of the body, and that stones are found within the coats of the bladder, and in the prostate gland where the urine has no access. Irritation excited in the bladder, he remarks, causes stones to be generated there, and as incrustations are formed upon foreign bodies in the bladder, so are they also in the mucous glands and membranes in other parts. Dr. A. makes use of other arguments to establish his assumption, but we have extracted those that appear to us the most forcible. We cannot help expressing surprise, that

the present author, Dr. Marcet, does not enter into the question of the modus operandi of calculous productions, with that par ticularity and precision which we should have expected from a man of so much scientific accuracy and philosophical acumen, as he is evidently endowed with. Dr. Austin carries his notion too far with regard to the mucous and membranous productions of stone; a more minute analysis of urinary concretions than had obtained in bis time, at once shews the analogy not to be so great as he assumed it to be with other membranous concretions, such as chalk stones in gout, and at the same time establishes their resemblance more fully to fluid urine; nevertheless, we are disposed to regard the secretions from the mucous membrane which lines the urinary organs and passages, as having a very considerable share in the formation of stone, and to infer that those substances and means which are employed to correct the calculous tendency, act in a considerable measure upon the actual secretions of the glandular parts to which we allude. Dr. Austin indeed very ingeniously conjectures, that the operation for the stone, proves often a radical remedy for the disease, not merely by extracting the calculus already formed, but by exciting a new action in the coat of the bladder, so as to obviate future depositions.

As it respects the remote causes of stone and gravel, or the constitutional dispositions and habits of life which combine to effect these concretions, inquiry has hitherto left us considerably in the dark. We know that the gouty diathesis and the tendency to gravel, are frequent concomitants, but they are by no means invariably so; the one and the other state and disposition often existing quite exclusively with regard to the exterior or immediately exciting causes of calculus, nothing certain or satisfactory has hitherto been ascertained. The use of what are called hard waters, has been conjectured to be influential towards the generation of stone; but beside that human calculus is very different from the several combinations of earthy substances which these waters are found to contain, it has been observed that those individuals are quite as subject to them who live con stantly on waters which are termed soft, as persons who have drunk of mineral and earthy springs through the whole of their lives. Dr. Marcet seems inclined to suppose, that there is a greater relation in calculous complaints to the functions of the skin, than has hitherto been conceived, aud he concludes the section of his work which is devoted to that inquiry to which we now advert, by making the following inferences."

In this early stage of the enquiry, and until a much greater num ber of documents than those I have been able to collect, shall have been procured, we should in vain attempt to connect the facts afforded by those reports, with any systematic view of the causes of calculous

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disorders. But I indulge in the hope that the present essay may be the commencement of an investigation, to which the results of subse quent researches on the subject will be gradually added. In the mean time sufficient evidence has already been obtained to shew, that in some establishments, both in this and other countries, a remarkable uniformity prevails in regard to the frequency of the disease, whilst in other instances a great discordancy is observable, and that none of the circumstances commonly suspected to influence this disorder, can satisfactorily account for this variety of results. This naturally leads to the suspicion, that the tendency to form urinary calculi must arise from some general causes, independent upon the peculiarity of food or beverage to which they have been usually ascribed; and since it appears that in hot climates, and especially between the tropics, these complaints are almost unknown. one is naturally led to connect this circumstance with the great changes in the urine known to arise from different conditions in the surface of the body, and to enquire whether amongst other causes there may not be some essential connection between the state of the cutaneous functions, and the greater or less prevalence of this class of disorders.'

1.

With respect to those several remedial processes which have been instituted with a view either to dissolve stone when formed, or to prevent the increase of the concreted substance, there cannot be a doubt that the question of their efficacy, must greatly depend upon the practicability of any solvent or corrective matter finding its way to the urinary organs; and if that be possible, the next object of inquiry will be, What are the constitu, ent ingredients of the particular substance to which our curative attempts are about to be applied? Now, that alkaline substances are capable of being conveyed to the urinary organs, and impart ing their specific properties to the secreted fluid, has been as certained beyond the possibility of a doubt. Among the late Dr. Whytt's cases, we find the following experiment, which, as being conducted by an individual who was himself the subject of the experiment, and a man of unquestionable veracity, it may not be amiss to record.

The Reverend Dr. Richard Newcomb, now Lord Bishop of Landaff, while drinking two English quarts of lime water daily, for the cure of a stone in the bladder, poured his urine every morning and evening upon a piece of human calculus weighing 31 grains; by of four months it was reduced to three pieces which in the space weighing in all six grains. Upon one of these pieces, weighing 2,31 grains, he caused to be daily poured for two months, the fresh urine of a person who drank no lime water, at the end of which time the piece of calculus was found to weigh, 2,56 grains, having increased in weight a quarter of a grain. This same piece being afterwards steeped in the Bishop's urine, (who continued to drink lime water as above) from June 24 to July 9, was in these few days quite crumbled into powder.'

One difficulty presents itself in reference to the solvent agency

of substances taken into the stomach; and it has been urged as an objection against the supposition of lithonthriptics possessing any specific virtue. It is this, that mild alkalies, as they are termed, or those alkaline substances which are combined with the carbonic acid, have appeared to mitigate the symptoms of stone with greater facility and effect than the pure or caustic alkalies, whereas it is these last which display their solvent properties upon lithic concretions out of the body, with by far the greatest activity. This objection, however, is satisfactorily met by the statement, that the carbonic acid of the mild alkalies, may, and does, by meeting with the acid of the stomach, become expelled or neutralized, and that thus the medicine is brought to precisely the same condition of efficacy as if it had been taken uncarbonated or pure; while it has this advantage when administered in a mild form, that it can be taken in a much larger quantity, and that, moreover, the neutralization of the acid in the first passages, corrects the constitutional tendency to fresh deposits of calcareous matter.

The principle then being admitted, that alkaline matter, when taken into the stomach, possesses at the very least some corrective and solvent property, (it being recollected at the same time, that urinary concretions occasionally happen, which are not acted upon by alkalies, but on the contrary, are only solvable in the mineral acids,) it follows of course to be considered, whether, and to what extent, these acid substances are capable of impregnating the urine with their specific influences. On this head; we shall extract the following observations of Dr. Marcet.

With regard to the acids,' says our Author, the question is not so easily resolved. For, as the urine is naturally acid, and especially containing portions of both the muriatic and sulphuric acids, which are those commonly used as medicines, any small increase of either of these acids in the urine, in consequence of their being taken into the stomach, cannot be so readily ascertained. It is how ever stated by some chemists, and in particular by Mr. Brande, that acids taken into the stomach, are actually capable of being conveyed into the bladder; and this he has more especially endeavoured to ascertain by experiment with regard to the carbonic acid. Unfortunately, however, although alkalies do certainly, and acids may possibly, reach the urinary passages, yet experience has shewn, that the quantity of either, thus conveyed through the circulation, is so sinall, that very little, if any impression, can be made on large pré-existing calculi with whatever freedom or perseverance these medicines may be used. But there is abundant evidence to prove, that we are able in many instances, to produce an effect sufficient to check the prevailing diathesis, and even sometimes to bring on a calculous deposit, depending upon an opposite state of the system; a change, which I have myself repeatedly witnessed.'

We have been induced to make the above extract, partly

for the sake of doing justice to the extreme candour, and unsystem-like freedom, with which the writer admits the limits of me dicinal operation, in the way of solvent efficacy; and partly with the view of impressing the necessity of early ascertaining the precise nature of those sabulous concretions, which are passed in a gra velly subject, before any curative plans are adopted, for the purpose of preventing their increase; since the common alkaline lithonthriptics, might, in the place of proving remedial, actually, in some cases, afford afresh pabulum to the disorder. Into the minutiae of these plans, we do not consider it as our province to enter; but we shall take occasion to make a short extract from a writer of celebrity, bearing upon the point of discrimination to which we are now adverting. It will be recollected, that we have remarked, in a former part of the present paper, that the lithic or uric acid calculi, are the most common species of concretions, and that these are soluble in alkaline menstruæ. In this case, alkaline medicines are called for, and will prove more or less efficacious. But in those kinds of calculi which are composed of earthy bases with phosphorie acid, it will also be recollected that the muriatic acid was said to be the agent of solution; but it may be now proper to add further, that lime and alkalies might not only be thrown away when applied to these concretions, but that the exhibition of these medicinals as just hinted, would in many cases be actually calculated to increase the evil they were intended to lessen, by furnishing that earthy substance in greater quantities, by which the base of the concretion is principally formed. The absurdity,' (says Dr. Pemberton, the author to whom we have just alluded,) of persevering in a plan of alkaline medicines to dissolve a calculus, which is not in the smallest degree acted upon by an alkali, but on the contrary by an acid, is sufficiently apparent. I am here alluding to the scheelian and fusible cal 'culi; the first sort being soluble in alkalies and not in the muriatic acid, the second, soluble in the muriatic acid, and not in the alkalies. The fusible calculus, or rather the fusible sand, (continues Dr. P.,) as mentioned by Dr. Wollaston, I am inclined to believe, is much more common than is usually suspected, and the benefit (he adds) obtained from an acid solvent in this species of calculus, I have observed, is much more rapid, than could be expected from the usual effects of repeated solvents in other cases of calculus.'

It is most probable, that in the instances which Dr. Pember ton adduces in support of this assumption, the benefit procured by the mineral acid, was referrible to its action on the first pas sages, and to its thereby correcting the tendency to sabulous deposite. But we must refrain from going further into practical detail. We shall therefore conclude our remarks, by recom mending both to the philosophical inquirer, and to the medical