Dr. Bird describes certain dumb-bell shaped crystals .(fig. SO ,b) with finely striated surfaces, as a variety of form of oxalate of iime. We have frequently seen such bodies, but cannot regard their chemical nature as established.
From a table, which we have drawn up from the daily record of 81 unselected cases (42 of each sex) in our wards at University College Hospital, the following inferences may be drawn Foreign to the natural constitution of the urine, cystin is of very rare occurrence as a morbid precipitate. It appears as a pale nearly white pulverulent matter, insoluble in water, in urine (cold and hot), and in acetic acid. It is soluble in ammonia, from which solution it may be obtained by evaporation in the.peculiar crystalline form (fig. 82), visible with the microscope only. Cystin is soluble without effervescence in nitric acid; from this solution silky crystals of aciculated shape and brilliant white colour may be obtained by evaporation. Treated with nitrate of potass, the sulphur (26 per 100 nearly) contained in the cystin passes to the state of sulphuric acid, discoverable by a salt of baryta. Cystin exhales a peculiar phos phorus-hke odour when burned on platina.
The crystalline form of cystin is the hexa gonal prism ; the crystal is transparent, more or less regular, and varies considerably in size (fig. 82).
Fig. 82.
5. The phosphate of ammonia and magnesia calculus (triple phosphate) is generally of oval or rounded shape, but may be of irregular form ; when constituting the entire substance of a calculus (which is rare), it is of small size usually ; its external colour is whitish ; its surface uneven and crystalline. Internally it is generally granular and opaque, though occasionally laminated and somewhat trans parent ; in the former case of porous texture, in the latter compact and dense, and of dirty 'white colour.
6. The neutral phosphate of lime calculus, remarkable for the snioothness of its extericr, is of pale brown colour, moderate size, and great rarity, — so much so that to the chance experience of Dr. Wollaston alinost alone are we indebted for what is known of its charac ters. It is composed of laminw, easily separ
able from each other, and striped transversely,.
7. The phosphate of anzmonia and magnesia and phosphate of linze (mixed phosphates or fusible) calculus is of irreg,ular shape, often of large size, white colour, and roughish surface. In the majority of cases its section looks like a piece of chalk of loose texture, being homo geneous, non-laminated, and minutely porous; in other instances it is lamellar, and between the laminw minute shining crystals of triple phosphate may often be detected. It rnarks the fingers or other bodies like chalk.
Phosphoric acid exists in healthy urine in combination with ammonia and magnesia, in such proportion as to form a perfectly soluble salt. If the proportion of base increases, the salt becomes insoluble, and, according to the amount of excess, is deposited either as the neutral or a bibasic triple phosphate.
The neutral phosphate of ammonia and mag nesia (the only one observed in urine at the moment of emission) occurs in white trans parent crystals of perfectly regular forms, re ferable to the right rectangular prism (fig.83).
These crystals are often mixed with amor phous powder, commonly composed of phos phate of lime, rarely of urate of ammonia. They are instantaneously soluble in weak acids, and the solution is precipitable by am monia in the form of the bibasic phosphate.
The bibasic phosphate of anzmonia and mag nesia does not appear to exist in urine, even the most strongly alkaline, at the moment of emission. But its crystals are developed with the progress of decomposition, and may be obtained from any urine by rapidly adding large quantities of ammonia. Microscopically (fig. 84) these crystals appear aciculated and grouped at angles of 60°, so as to resemble a pinnate or bipinnate leaf.
Phosphate of lime occurs as an amorphous powder ; very soluble in acids, it does not effervesce under their action, like the urate of ammonia, nor, like that salt, furnish crystals of uric acid under the same circumstances ; when the phosphate has been dissolved in an acid, ammonia precipitates a white amorphous mass from the solution.