Gravel , small stones, commonly intermixed with sand, and sometimes with clayey or calcareous earth. Such a mixture constitutes the principal portion of the drift formation; and where this prevails, the surface of the country is often covered to unknown depths with deposits of sand and gravel. It forms hills throughout New England, and nearly the whole of Long Island is covered with it. (See Diluvium.) It is of more recent formation wherever rocks, especially the granitic, are comminuted by joint action of atmospheric and fluviatile agents, and their materials are gathered in the bed and banks of swift running streams. On the beaches of seas and lakes, the gravel, piled up in beds of coarse pebbles and washed clean of sand and all earthy mat-ters, is called shingle.
Gravel , substances consolidated and precipitated from the urine within the body, in certain diseased conditions of the system, differing from calculi by their small size, and generally voided without surgical interference. (See Calculi.) The appearance of gravel is important as evidence of a disposition to calculous deposits, and as indicating the proper treatment. When the disposition exists, anything which obstructs the passage of urine favors the precipitation of gravel. There are three kinds of gravel, as there are three principal forms of calculi, viz. : the lithic, the oxalic, and the phosphatic. Lithic or uric acid, a highly nitrogenous compound, exists normally in the urine in combination with soda; if the urine be abormally acid, the lithic acid will be precipitated in a crystalline form, constituting the lithic or red gravel; lithic acid when pure is white, but in human urine it assumes the tint of its coloring matter, which causes it to look like Cayenne pepper. The urine containing this gravel is generally acid, high-colored, scanty, but clear; in what is called a "fit of the gravel," this acid is precipitated in large quantity, accompanied by fever, pains shooting from the loins to the bladder, frequent and scalding micturition, etc.
The causes which predispose to the excessive formation of lithic acid have been detailed in the article Gout, with which disease gravel is intimately connected; it will be sufficient to say here that the use of highly nitrogenous food and stimulating drinks, and sedentary or slothful habits, are very likely to induce both gout and lithic acid gravel. Though not unfrequently occurring in children, gravel is most common between the ages of 40 and 65; it is comparatively rare in warm climates, or in persons living chiefly on vegetable food. On the principles of Lie-big, the great indication for the treatment of the red gravel is to promote the action of oxygen on lithic acid so as to cause its conversion into urea and carbonic acid, and its consequent escape from the system through the urine and the perspiration; in other words, to take in an increased supply of oxygen by exercise in the open air, by preparations of iron, and by the nitro-muriatic acid; to moderate the quantity of highly nitrogenous food, avoiding that containing much starch and sugar, as well as malt and fermented liquors; to secure a healthy action of the skin by suitable clothing and attention to cleanliness; to remove all intestinal obstructions, and to neutralize acidity, if necessary, by the administration of alkalies. - The lithic acid gravel may be regarded as the sign of an inflammatory or congestive habit, but the next form, or the oxalic acid gravel, belongs to an irritable or nervous constitution, and is usually accompanied by a dry skin, dyspepsia, boils, carbuncles in advanced life, and nervous exhaustion or despondency; the urine is transparent, pale greenish yellow, of moderate specific gravity, and free from sediments, but containing minute crystals of oxalate of lime.
The causes of this diathesis are such as produce dyspepsia, nervous debility, and hypochondriac diseases: residence in malarious districts, and unwholesome vegetable food. The treatment is very similar to that for lithic acid gravel, it being remembered that in this case the system craves less oxygen; distilled water is advised in order that lime may not in this way be introduced into the system and endanger the formation of mulberry calculi; alkalies, with ammonia, tonics, and the mineral acids, are required according to circumstances. Oxalate of lime deposits, however, are usually much less abundant and less irritating than those of uric acid, and, as a general rule, are less important indications of an unhealthy state of the system. The white gravel may be either the ammoniaco-magnesian phosphate or the phosphate of lime, or the mixture of the two. The earthy phosphates are naturally held in solution by the acid reaction of the urine; and when this is neutralized or replaced by an alkaline reaction, these phosphates are precipitated in the form of a white amorphous powder. If the urine become ammoniacal, a new compound is formed, namely, the triple phosphate of magnesia and ammonia.
This substance has the form of three-sided prismatic crystals, sometimes large enough to be distinguished by the naked eye. The phosphatic diathesis is generally seen in pale and weak persons, complaining of nervous exhaustion, as Dr. Prout maintains, on account of the great consumption of phosphorus in nervous diseases; it may be produced by excessive fatigue of body or mind, intense study, unwholesome food, weakening medicines, and chronic urinary affections. The treatment should consist of tonics.