The stellar and foliaceous crystals are not all formed by crossing only, some being appositions of groups of crystals in the prolongations of the axes of a central crystal. In this way the most fanciful forms are obtained.

The crystals of triple phosphate. polarize light, and then appear tinted with prismatic colours. When seen in a sunbeam reflected through the polarizing microscope, they appear the finest objects for studying the phenomena of polarization.

Chemical properties.—When kept in water the triple phosphate disintegrates, the surface of the crystals becomes corroded, and at last there is nothing left but amorphous phosphate of magnesia. This corrosion is prevented by the presence of free ammonia, which makes them quite insoluble in water, and is therefore eligible as a preserving fluid for microscopical specimens. When the transparent crystals are exposed to a boiling heat, they lose water of crystallization and become opaque. They are easily soluble in acetic acid, and from this solution may be obtained again by excess of ammonia.

When heated with a solution of potash, the triple phosphate is decomposed, the potash combining with the phosphoric acid and setting free the ammonia and the magnesia. The former volatilizes, and may be detected by the smell, while the magnesia is precipitated.' (PO,+2MgO + NIO + 12HO) + 2KO = (PO, + 2KO + HO) + NH ̧ +2MgO + 12HO.

Earthy Phosphates in Calculi.

Not quite 10 per cent. of all calculi have a nucleus of mixed phosphates. But these substances enter into the composition of about 34 per cent. of all calculi, forming either their body, one or more layers, or the crust. This shows that the presence of deposits of mixed phosphates in the urine scarcely ever gives rise to the formation of calculus, but that the presence in the bladder of other calculi frequently causes a deposit of phosphates to be formed around them, in which respect every calculus is nothing else than a foreign body.

Twenty-two out of 233 in Guy's Hospital Museum. Dr. Golding Bird gives the number of calculi preserved there as 374, which is inclusive of 142 calculi taken from one individual. For calculating the comparative frequency of calculi, such a mode of reckoning is unavailable. We therefore take the 142 as 1, and then we have 374-141=233.

Prout found the proportion of phosphate of lime calculi to the whole number contained in various museums as 1 to 117. The proportion of calculi composed of pure triple phosphate was 1 to 126. The relative proportion of the mixed phosphates he put as 1 to 121. The general proportion of all the calculi, arranged under the heads of the phosphates in different museums, he found as 1 to 10. In alternating calculi, the phosphates succeeded to uric acid in the proportion of 1 to 91. The ratio in which the phosphates succeeded to urate of ammonia (and soda) was as 1 to 124; and in which the phosphates succeeded to the oxalate of lime was as 1 to 7. On the contrary, three instances only occurred in which the uric acid, or urate of ammonia, succeeded to a phosphate; and the proportion in which the oxalate of lime succeeded to the phosphates was as 1 to 253 only. The general proportion in which the phosphates succeeded to the other ingredients, was as 1 to 4.

From these facts, Prout deduced the general law that, in urinary calculi, a decided deposition of the mixed phosphates is not followed by other depositions.

Calculi of phosphate of lime have mostly a smooth surface, and are composed of concentric layers, which, when the calculus is broken, separate from each other with great facility, forming detached crusts. These are almost infusible before the blowpipe, requiring for fusion so intense and prolonged a heat, that few can succeed in fusing it (Bowman). The chemical characters of these calculi are those of phosphate of lime, as described above.

Calculi composed entirely of triple phosphate are generally crystalline, or consisting of aggregated prismatic crystals; they often contain cavities filled with the largest and most perfect crystals of triple phosphate, or have their surface covered with a smaller variety of them. Specimens of this kind are contained in the Museum of the College of Surgeons.

Before the blowpipe, the triple phosphate gives off the smell of ammonia, swells up, gradually becomes gray, and ultimately fuses.

Calculi composed of phosphate of lime and triple phosphate are commonly called fusible calculi, from the readiness with which they fuse before the blowpipe, giving off ammonia and water, and leaving a mixture of phosphate of lime and pyrophosphate of magnesia.

Physiological quantities of Earthy Phosphates in the Urine.

The proportion in which the phosphate of lime in the urine stands to the phosphate of magnesia has been determined by Kletzinsky' to be about two to one; namely, 67 parts of phosphate of lime and 33 parts of phosphate of inagnesia in 100 parts of mixed earthy phosphates precipitated from healthy urine.

The average amount of phosphates of the alkaline earths discharged by a healthy man in twenty-four hours, has been determined by Bencke to be 12 grammes. Under ordinary diet, Lehmann discharged 109 grammes; Boecker,3 1:43 grammes. These observations give, as the average of mixed phosphates during twenty-four hours, 128 grammes.

Mosler and Hegar determined the quantity of earthy phosphates by calculation from their phosphoric acid. The former made two series of observations upon himself, the first series comprising six days in April, the second four days in October. His results were as follows:

Observations of the quantity of Phosphoric Acid combined with Earths in the Urine.

In other healthy individuals, Mosler found the average per hour of PO, to fluctuate between 0015 and 0.019 grammes. Hegar found from observations, extending over eight days, that he discharged 1:31 grammes of phosphoric acid in combination with earths. Six months afterwards, the average of four days was only 0.902 grammes of PO. Neubauer determined directly the amount of lime and mag

'Heller's Archiv,' 1852, p. 270, et seq.

Zur Physiol. und Pathol. des Phosphors. und Oxals. Kalkes,' Göttingen, 1850.

nesia discharged by two healthy persons. His results are arranged in the following table:

Observations of the quantity of Lime and Magnesia discharged during twenty-four hours.

From all the observations taken together, it follows, that the amount of earthy phosphates in the urine varies in different individuals, and in the same individuals at different times. A general average for any given weight of individual can therefore not be drawn at present. It can only be ob tained by extended observations on the urine, taking into consideration the quantities of earths ingested with the food, and those discharged by way of the bowels.

The influence which different qualities of food have upon the quantity of earthy phosphates discharged by the urine is well illustrated in the experiment of Lehmann. As we have already stated, when eating mixed food, his average amount of earthy phosphates was 1.09 grammes. But when he restricted himself to animal diet, the amount rose to 3.56 grammes, being more than three times his ordinary average.

Pathological indications.

1. The presence of earthy phosphates in the urine is indicative of the alkaline condition of that fluid.

2. If the precipitate of earthy phosphates is entirely amorphous, we may conclude that the alkali which caused it was not ammonia.

3. If, however, the precipitate contains crystals of triple phosphate, it indicates the presence of ammonia, arising most probably from decomposition of urea.

An excess or deficiency of earthy phosphates in the urine can only be ascertained by quantitative chemical analysis. The

mere presence in the urine of a deposit of this kind, or its appearance in the urine on heating, is by no means indicative of an excess, as is yet too commonly believed. The originators of the term phosphatic diathesis and phosphuria, and their followers, linked a series of the most varied disorders together under this term, which had nothing in common but one symptom, namely, alkaline urine. The following facts and considerations may perhaps serve to explain some opinions, which, by the weight of authority, are rather widely circulated, but nevertheless require a thorough reformation.

Animal diet has a tendency to increase the acidity of the urine; vegetable diet easily makes it alkaline. The dyspeptic, therefore, eating little or no meat, will easily cause his urine to be alkaline by eating a little fruit, for which he not unfrequently has a longing. But even if no fruit has been partaken of, and but little meat, the secretion may be alkaline; in the former case from the presence of carbonates, in the latter from that of alkaline phosphates from the blood, which the free acid has not been sufficient to transform into acid salts.

What want of appetite for animal food causes in the dyspeptic patient, want of animal food causes in poor, old people. The alkaline urine of the octogenarian dependent upon parochial relief, is the consequence of his not being able to afford meat once a week. Hence, in these cases, the acidity of the urine is restored by a proper allowance of meat.

The anæmic girl and the diabetic patient are instances of the same character. In the former, the phosphates may be altogether absent for a day or two, so that the urine, being alkaline, will form no deposit. Meat diet will soon restore acidity and phosphates. In diabetic patients, phosphate of lime is sometimes altogether absent, and the alkaline urine deposits the triple phosphate only. Lehmann observed such a case. The glittering crystalline deposit of triple phosphate contained no trace of lime. We may here observe, that the microscopical analysis is not sufficient to prove the absence of phosphate of lime. For Vogel (p. 203) observes that deposits of the latter salt are often so transparent, and their outlines are so little defined, that when mixed with the triple phosphate they are easily overlooked, unless the observer takes particular care in illuminating his object. It is for this reason, that we cannot take any notice of statements regarding the occurrence of deposits of the triple phosphate, unmixed with phosphate of lime, which are not sustained by exact chemical tests.

Urine becomes alkaline when retained in the bladder for