If a stone is obstructed in its passage through the urethra after bleeding, an emollient clyster and an anodyne draught will be proper; common emulsion should be drank freely, and if the patient is placed in a warm bath presently after the clyster is administered, the stone often escapes.

If the stone stick in the neck of the bladder, and require an operation for its extraction, introduce two fingers into the anus, to detain the stone until the incision is made through the perinaeum upon it. After the operation, as well as for some days before, Heister advises the patient to drink as sparingly as possible, that the wound may not be irritated by the urine. To guard against this inconvenience, a canula may be introduced beyond the wound, and kept in the urethra until it is healed. In whatever part the stone is lodged, the incision must be made in the course of the urethra, and the wound in the skin parallel to that in the urethra. When the stone is extracted, close the wound, and keep its lips together, by first laying on it a pledget of lint spread with some digestive ointment, then secured with slips of plaster, as directed for the dry suture.

It has been lately recommended to inject the caustic alkali into the bladder, diluted in any mucilaginous fluid; and experiments have been adduced to show, that the bladder can bear, without inconvenience, a sufficient quantity to render the urine an active solvent of calculus. On this subject, however, we would lay down no precise rule; for the bladder differs greatly in irritability in different persons, and it will be proper to begin with a small proportion. The plan is too obviously useful to be neglected, and experience may enable us to give a further account of its success in some future article. We may add, however, in this place, that weak vinegar, which may with safety be injected into the bladder of a horse, is found, from the experiments of

Vauquelin and Fourcroy, an effectual solvent for the calculus of that animal.

We shall conclude this article with some comparative remarks on the human and animal calculi, from a second Memoir of M. Fourcroy, in a subsequent volume of the Annals of the National Museum, and with an analysis of the other human calculi.

The difference between the human urinary calculus, and those of other domestic animals, is truly singular. The renal and vesical calculi of the horse, the ox, the hog, and even of the rat and rabbit, in whom calculi are frequently found, consist only of carbonate of lime, connected by an animal gluten. Once M. Vauquelin suspected that he discovered the uric acid in the calculus of a tortoise, but it was not in sufficient proportion to render it certain. M. Fourcroy and his associates constantly found a striking analogy between the nature of the urine, and that of the calculus of the domestic mammalia. But, though the urine of horses does not contain phosphat of lime, they found it in the sweat, when dried on the hair; and, from Mr. Hatchet's experiments, it will appear that nature is uniform in her productions. The same substances are formed in the animal economy, deposited only on different organs. Many of the bezoars of different forms and colours chiefly consist of calcareous phosphat, but they seldom contain the acid phosphat, and are consequently formed in the intestines; which is sufficiently proved by their nuclei, which are often the kernels of fruit, and sometimes small branches. In these animals, therefore, the substance, not carried to the kidneys, concretes in the intestines.

In the domestic animals, and those wild ones confined to the menageries, intestinal concretions, from the size of a large hen's egg to that of an ostrich, are often found in the coecum. Those in the horse are of a greyish colour, formed of prismatic radii, without any distinct strata: the surface consists of irregular crystals worn down by attrition, with cavities between them. All these bezoars are composed of an ammoniaco mag-nesian phosphat, a substance lately discovered in barley and oats, as well as in some of the legumina, though in a less proportion. We thus find the source of these concretions; and their nuclei are generally some undigested seed, or a bit of straw. This salt does not naturally concrete in man; and it requires some additional substance or circumstance to assist its appearance, when it is discovered in the calculi of the kidneys and bladder. Nor is it easy to say, why some of the bezoars of wild animals should consist of the ammoniaco magnesian phosphat, while others contain the phosphat of lime only.

Dr. Pearson has analysed also the calculi of many animals. That of a dog was found, by him, to contain phosphat of lime and ammonia, with some animal matter: that of a rabbit yielded chiefly carbonate of lime, with common animal gluten, and perhaps a small proportion of phosphoric, but no uric acid: those of horses, whether vesical or intestinal, afforded phosphat of lime and ammonia, with animal matter, which melted like super phosphat of lime, after separating the animal substance and ammonia by burning. A large quantity of matter found in the bladders of horses not crystallized, each of several pounds weight, was carbonate of lime with the animal fluid. Bertholdi found alculus of a pig, which was nearly twice as heavy as distilled water. to consist of phosphat of lime.

Arthritic calculi were once supposed to be chalk, then to resemble the earth of bones; to be insoluble in acids, to be soluble in them, or to be soluble only in the nitrous acid. Various other discordant opinions were entertained, till Dr. Woolaston, in the Philosophical Transactions for 1797, gave us more distinct ideas or the subject: he found them to consist of the lithic acid ana soda. We thus find the foundation of the use of antacids, and perhaps of bitters, in cases of gout.

The calculi of the pineal gland were supposed by many authors to be imaginary. Sabulous concretions, how ever, in this part have been often discovered; and Dr. Woolaston, by a delicate chemical test, has discovered them to consist of phosphorated lime. This is, how ever, a refinement only, for these concretions are not connected with any concurrence of symptoms so as to form a disease.