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form two atoms of Carbonate of Ammonia. The causes which determine this conversion are various. Among them may be cited:

In cases of uræmia, it is an interesting question, whether the morbid effects are due to the presence of the unchanged urea in the blood, or to its conversion into Carbonate of Ammonia. A careful proving of these two substances would aid us in deciding the point, and might af ford valuable hints in treatment.

Uric-acid exists ready formed in the blood, and is found in healthy urine in the form of Urate of Ammonia. Johnson supposes that it forms less than part of healthy human urine. Prout supposes that it is derived from the decomposition of the albuminous tissues; while Liebig maintains that it results from the decomposition of the nitrogenous tissues.

Ammonia is another constituent of healthy urine, and is found in the form of Urate of Ammonia. 1000 parts of urine contain from 2.16 to 2-19 parts of Ammonia. Hippuric acid is another healthy constituent of healthy urine, and forms about part of the entire quantity excreted. This acid abounds in carbon, and is usually abundant in consumptive and other patients, whose blood is imperfectly decarbonized.

The sulphates of healthy urine are chiefly those of Soda and Potash, although Sulphates of Lime, Magnesia, and Ammonia are usually present in minute quantities. They are supposed to be derived in part from the metamorphoses of the tissues, and in part from the food. Unoxidized Sulphur is also found in the urine, but its precise combinations are not yet fully understood. According to Ronalds, from two to five grains of Sulphur are excreted daily.

Phosphates of Potash, Soda, Lime, Ammonia, and Magnesia, are also found in minute quantities as constituents of healthy urine. They are also derived from the changed tissues and from food. Unoxidized Phosphorus, in minute quantities, is also present in normal urine.

From the analysis of normal urine we observe, that traces of the Chlorides of Sodium, Potassium, Lime, Ammonia, and Magnesia are present, and that they are derived chiefly from the food.

Color.-The color of healthy urine has been termed by different writers, amber-colored, straw-colored, sherry-wine-colored, yellow, &c. We know of no term truer or more expressive, than amber-colored. As already observed, in infants, females, aged persons, and in certain anæmic conditions, the urine is more watery, and consequently paler in color.

Red urines generally indicate an excess of acid, a high specific gravity, and the presence of a large proportion of solids. Many causes may contribute to the production of highly-colored urine in health; like an undue elimination of the water through the pores, abstinence from drinks, and the use of highly-nutritious and highly-seasoned food.

The use of certain drugs and beverages may also give a red tinge to the urine. Red urine is also an accompaniment of many abnormal conditions, like fevers, dropsies, and maladies characterized by a rapid decomposition of the tissues and the blood. The acid which gives the red color to urine is the Bi-phosphate, or Acid-phosphate of Lime, and not uric or lactic-acid, as is generally supposed.

Deep-yellow urine indicates the presence of bile.

Dark urines-brown, blue, or black, are observed during the pro gress of many malignant diseases, and are due to rapid morbid change in the tissues and to a decomposition of the blood. Black urine is sometimes voided after long-continued epileptic convulsions, in consequence of protracted and spasmodic muscular contraction. Brown, red, or blackish urine is sometimes due to the presence of blood. Under the microscope, the globules appear deformed and irregular, and they finally disappear. Amorphous fragments are then found similar to

those observed in albuminous urine.

Turbid urine indicates, first, the presence of mucus with diminished density, paler color, and, after standing a few hours, a separation into an upper and clear layer, and a lower and turbid and opaque one, with ammoniacal odor, in consequence of the decomposition of urea into carbonate of ammonia, which mucus rapidly determines. Second, turbid urine is also caused by the presence of pus. Such urine is less dense than natural, of a greenish color, clears soon after emission, and deposits a thick, whitish, and foetid sediment. Like mucus, it hastens the conversion of urea into carbonate of ammonia. Under the microscope, pus-cells are observed in the upper or transparent stratum, at first very numerous, but, after ten or twelve hours, (as in case of bloodglobules), they disappear, and a kind of granules are found in their stead.

Sediments.-The sediment of acid urines is composed of uric-acid crystals, acid urates of soda, ammonia or lime. The sediment of alkaline urines consists of carbonate and oxalate of lime, and ammoniacomagnesium phosphates. Sediments of pus, mucus, and blood-globules are not unfrequently found. The composition of urinary sediments is so various, arising from the decomposition of the urine and its waters, that we can only allude to them here, and refer the reader to Becquerel, On the Urine, and to Thudicum's Pathology of the Urine, for more minute information upon the subject.

Acid Urine.-Normal urine is generally acid, as may be proved by test-paper. By standing it becomes more acid, and passes through an acid fermentation, resulting in the separation of reddish-yellow rhomboid-shaped crystals under the microscope. Acid urine is deep-colored and dense, and the acidity is derived from the bi-phosphate, or acidphosphate of lime, and not, as is commonly supposed, from the uric or

lactic acid. Liebig attributes the acidity of the urine to the presence of acid-phosphate of soda. Where great accuracy is not requisite, the urine may be tested for acidity with litmus paper. The tests should be applied at different periods of the day, and an average drawn; since the degrees of acidity are constantly changing from the food and drink consumed, from fasting, exercise, &c.

Neutral Urine.-This is only ordinary urine very much diluted, like that which is observed in anæmic subjects.

Alkaline Urine.-This is rarely observed. Its sources are blood, pus, and the decomposition of urine or carbonate of ammonia in the bladder-the last being the most frequent. The most frequent determining cause of this alkalinity is the action of the oxygen of the air upon the substances cited. But the urine may be alkaline at the instant of its secretion in the kidney. After standing for a considerable period, acid urine sometimes becomes alkaline, in consequence of the decomposition of urea, and the development of carbonate of ammonia, ammonio-magnesian phosphates, and phosphate of lime. This result may likewise be produced by boiling urine for several hours.

COMPOSITION OF URINE.-When we consider the various circumstances which are in constant operation to modify the composition of urine, it will not appear surprising that chemists have presented us with such diverse analyses. The urines of the claret-drinking Frenchman, of the beer and port-drinking Englishman, of the lime-water drinking Yankee, and of the fruit-consuming denizens of tropical climates, must of necessity present great diversities in chemical composition. Even under any circumstances, the variety of food and drinks, atmospheric changes, habits of exercise, mental emotions, excessive mental or physical exertion, continual modifications are occurring in the composition of the urine. It is evident, therefore, that any analysis which may be presented must be regarded as only an approximation to the actual result.

We place before our readers an analysis of Becquerel, quoted from Johnson's "Diseases of the Kidney" p. 48, and another from Berzelius. "This analysis of Becquerel was adopted by Dr. Prout as being the most accurate. Dr. Prout took as a standard, thirty-five ounces of sp. gr. 1020, and employing M. Becquerel's data as the basis of his calculations, he obtained the results which are shown in the following table; the proportion of solids and liquids being thirty-three of the former to 967 of the latter."

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Berzelius gives us the following table as the

COMPOSITION OF 1000 PARTS OF URINE.

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10.167

8.135

1000.000

933.

30.10

1.

3.71

3.16

2.94

4:45

1.65

1.50

17.14

0.32

1000.000

=

77 to 82

100

SOLIDS OF NORMAL URINE-Urea. Chemical composition: C2 H4 N2 O2 60., sp. gr. 1.35. Of the solid constituents of healthy urine, urea forms from 12 part. It forms flat quadrilateral prisms, with aspect and taste like Nitre. It belongs to the class of organic bases, and forms crystalizable compounds with several of the acids; is soluble in five parts of cold or two parts of boiling alcohol-in its own weight of cold water, and in every proportion of boiling water; is insoluble in ether; is permanent in the air; fuses at 250° F., and at a higher temperature yields by spontaneous decomposition, ammonia, cyanate of ammonia, and dry solid cyanuric-acid. According to Johnson, 270 grains, or more than half an ounce of urea is excreted by a healthy man in twenty-four hours. It readily results from the transformations of various azotized matters, and, when not removed by the kidneys, it accumulates in the blood, and appears in the saliva, the bile, the gastric secretions, in nearly all the humors, and is so abundant in the sweat as to form, after spontaneous evaporation, a blueishwhite crust, especially upon the face. The quantity of urea is in VOL IL-2.

creased by all causes which determine rapid metamorphoses of the tissues. Its prolonged retention in the blood gives rise to what is termed uræmic poisoning, to which we shall refer hereafter.

For excellent methods of ascertaining the absolute quantity of urea in urines, we refer the reader to Thudicum's work on the "Pathology of the Urine," pp. 52, 67, and 69-" Methods of Liebig, Bunsen, and Davy." When the quantity of excreted urea continues above or below the natural standard for any considerable period, disease may be inferred. Among the causes which determine its diminution in the urinary secretion are insufficient food, impaired digestion, chronic maladies, anæmic conditions and diseases of the convoluted tubes of the cortex of the kidneys.

The principal causes which form the excretion of an excess of urea, are the assimilation of large quantities of nutritious food, the use of stimulants, febrile disorders, and general activity of the circulatory and digestive functions.

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2

Uric-acid.-Chemical composition: C10 H4 06 N4 C10 H2 04 N4 +2HO. Pure uric-acid, according to Brande, is a "soft, white, crystalline powder; it is insipid and inodorous; it reddens moistened litmus paper. It is almost insoluble in cold water (requiring, according to Bensch, from 11,000 to 15,000 parts), but soluble in between 1,800 and 1,900 parts of boiling water; it is insoluble in alcohol and in ether." When it is decomposed by heat it yields carbonate of ammonia, hydrocyanic acid, empyreumatic oil, cyanuric acid, urea, and carbon. It forms 468 in 1000 parts of normal urine, according to Becquerel. The average amount discharged by a healthy man in twenty-four hours is stated by Becquerel to be from 0.49 to 0.56 grammes. The proportions, however, may vary much in different individuals without any impairment of the health-such variations depending upon the quantity and quality of food and drink consumed, habits of life, &c.

Uric acid in combination with one or more bases-ammonia, soda, or lime is one of the most common sediments of the urine. Uricacid, being insoluble in the blood, can only exist in this fluid in the form of a urate-chiefly urate of soda-and is separated by the kidneys, passes to the pelvis of the kidneys, to the bladder, and thence out of the body as a urate of soda. But, during the passage of the latter through the urinary organs, portions of it are often decomposed, and uric acid set free by the free phosphoric and lactic acids of the urine. This decomposition may occur in the kidney, in the bladder, or after the emission.

In order to ascertain whether the urine holds in solution a urate, we add to it either nitric, acetic, or muriatic acid. If uric acid is speedily precipitated, we infer the presence of a large quantity of the urate;

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