I. PHYSICAL EXAMINATION
I. PHYSICAL EXAMINATION
1.Quantity.—The quantity passed in twenty-four hours varies greatly with the amount of liquids ingested, perspiration, etc. The normal may be taken as 1000 to 1500 c.c., or 40 to 50 ounces.
The quantity is increased (polyuria) during absorption of large serous effusions and in many nervous conditions. It is usually much increased in chronic interstitial nephritis, diabetes insipidus, and diabetes mellitus. In these conditions a permanent increase in amount of urine is characteristic—a fact of much value in diagnosis. In diabetes mellitus the urine may, though rarely, reach the enormous amount of 50 liters.
The quantity is decreased (oliguria) in severe diarrhea; in fevers; in all conditions which interfere with circulation in the kidney, as poorly compensated heart disease; and in the parenchymatous forms of nephritis. In uremia the urine is usually very greatly decreased and may be entirely suppressed (anuria).
2.Color.—This varies considerably in health, and depends largely upon the quantity of urine voided. The usual color is yellow or reddish-yellow, due to the presence of several pigments, chiefly urochrome. In recording the color Vogel's scale (seeFrontispiece) is very widely used, the urine being filtered and examined by transmitted light in a glass three or four inches in diameter.
The color is sometimes greatly changed by abnormalpigments. Blood-pigment gives a red or brown, smoky color. Urine containing bile is yellowish or brown, with a yellow foam when shaken. It may assume a greenish hue after standing, owing to oxidation of bilirubin into biliverdin. Ingestion of small amounts of methylene-blue gives a pale green; large amounts give a marked blue. Santonin produces a yellow; rhubarb, senna, cascara, and some other cathartics, a brown color; these change to red upon addition of an alkali, and if the urine be alkaline when voided may cause suspicion of hematuria. Thymol gives a yellowish-green. Following poisoning from phenol and related drugs the urine may have a normal color when voided, but becomes olive-green to brownish-black upon standing. Urine which contains melanin, as sometimes in melanotic sarcoma and, very rarely, in wasting diseases, also becomes brown or black upon long standing.
3.Transparency.—Freshly passed normal urine is clear. Upon standing, a faint cloud of mucus, leukocytes, and epithelial cells settles to the bottom. Abnormal cloudiness is usually due to presence of phosphates, urates, pus, blood, or bacteria.
Amorphous phosphatesare precipitated in neutral or alkaline urine. They form a white cloud and sediment which disappear upon addition of an acid.
Amorphous uratesare precipitated only in acid urine. They form a white or pink cloud and sediment ("brick-dust deposit") which disappear upon heating.
Pusresembles amorphous phosphates to the naked eye. Its nature is easily recognized with the microscope, or by adding a strong solution of caustic soda to the sediment, which is thereby transformed into a gelatinous mass (Donné's test).
Bloodgives a reddish or brown, smoky color, and may be recognized with the microscope or by tests for hemoglobin.
Bacteria, when present in great numbers, give a uniform cloud which cannot be removed by ordinary filtration. They are detected with the microscope.
The cloudiness of decomposing urine is due mainly to precipitation of phosphates and multiplication of bacteria.
4.Reaction.—Normally, the mixed twenty-four-hour urine is slightly acid in reaction, the acidity being due to acid salts, not to free acids. Individual samples may be slightly alkaline, especially after a full meal. The reaction is determined by means of litmus paper.
Acidity is increased after administration of certain drugs, and whenever the urine is concentrated from any cause, as in fevers. A very acid urine may cause frequent micturition because of its irritation. This is often an important factor in the troublesome enuresis of children.
The urine always becomes alkaline upon long standing, owing to decomposition of urea with formation of ammonia. If markedly alkaline when voided, it usually indicates such "ammoniacal decomposition" in the bladder, which is the rule in chronic cystitis, especially that due to paralysis or obstruction. Alkalinity due to ammonia (volatile alkalinity) can be distinguished by the fact that litmus paper turned blue by the urine again becomes red upon gentle heating.Fixed alkalinityis due to alkaline salts, and is often observed during frequent vomiting, after the crisis of pneumonia, in various forms of anemia, after full meals, and after administration of certain drugs, especially salts of vegetable acids.
5.Specific Gravity.—The normal average is about1.017 to 1.020. Samples of urine taken at random may go far above or below these figures, hence a sample of the mixed twenty-four-hour urine should always be used.
Pathologically, it may vary from 1.001 to 1.060. It islowin chronic interstitial nephritis, diabetes insipidus, and many functional nervous disorders. It ishighin fevers and in parenchymatous forms of nephritis. In any form of nephritis a sudden fall without a corresponding increase in quantity of urine may foretell approaching uremia. It ishighestin diabetes mellitus. A high specific gravity when the urine is not highly colored should lead one to suspect this disease. A normal specific gravity does not, however, exclude it.
The specific gravity is most conveniently estimated by means of the urinometer—Squibb's is preferable (Fig. 14). It is standardized for a temperature of 77° F., and the urine should be at or near that temperature. Care should be taken that the urinometer does not touch the side of the tube, and that air-bubbles are removed from the surfaceof the urine. With most instruments the reading is taken from the bottom of the meniscus.
One frequently wishes to ascertain the specific gravity of quantities of fluid too small to float an urinometer. A simple device for this purpose, which requires only about 3 c.c. and is very satisfactory in clinical work, has been designed by Saxe (Fig. 15). The urine is placed in the bulb at the bottom, the instrument is floated in distilled water, and the specific gravity is read off from the scale upon the stem.
6.Total Solids.—An estimation of the total amount of solids which pass through the kidneys in twenty-four hours is, in practice, one of the most useful of urinaryexaminations. The normal for a man of 150 pounds is about 60 grams, or 950 grains. The principal factors which influence this amount are body weight (except with excessive fat), diet, exercise, and age, and these should be considered in making an estimation. After about the forty-fifth year it becomes gradually less; after seventy-five years it is about one-half the amount given.
In disease, the amount of solids depends mainly upon the activity of metabolism and the ability of the kidneys to excrete. An estimation of the solids, therefore, furnishes an important clue to the functional efficiency of the kidneys. The kidneys bear much the same relation to the organism as does the heart: they cause no direct harm so long as they are capable of performing the work required of them. When, however, through either organic disease or functional inactivity, they fail to carry off their proportion of the waste-products of the body, some of these products must either be eliminated through other organs, where they cause irritation and disease, or be retained within the body, where they act as poisons. The great importance of these poisons in production of distressing symptoms and even organic disease is not well enough recognized by most practitioners. Disappearance of unpleasant and perplexing symptoms as the urinary solids rise to the normal under proper treatment is often most surprising.
When, other factors remaining unchanged, the amount of solids eliminated is considerably above the normal, increased destructive metabolism may be inferred.
The total solids can be estimated roughly, but accurately enough for most clinical purposes, by multiplying the last two figures of the specific gravity of the mixedtwenty-four-hour urine by the number of ounces voided and to the product adding one-tenth of itself. This gives the amount in grains. Häser's method is more widely used but is less convenient. The last two figures of the specific gravity are multiplied by 2.33. The product is then multiplied by the number of cubic centimeters voided in twenty-four hours and divided by 1000. This gives the total solids in grams.
7.Functional Tests.—Within the past few years much thought has been devoted to methods of more accurately ascertaining the functional efficiency of the kidneys, especially of one kidney when removal of the other is under consideration. The most promising of the methods which have been devised are cryoscopy, the methylene-blue test, and the phloridzin test. It is doubtful whether, except in experienced hands, these yield any more information than can be had from an intelligent consideration of the specific gravity and the twenty-four-hour quantity, together with a microscopic examination. They are most useful when the urines obtained from separate kidneys by segregation or ureteral catheterization are compared. The reader is referred to larger works upon urinalysis for details.
Cryoscopy, determination of the freezing-point, depends upon the principle that the freezing-point of a fluid is depressed in proportion to the number of molecules in solution. To have any value, the freezing-point of the urine must be compared with that of the blood, since it is not so much the number of molecules contained in the urine as the number which the kidney has failed to carry off and has left in the blood, that indicates its insufficiency.
In themethylene-blue testof Achard and Castaigne a solution of methylene-blue is injected intramuscularly, and the time of its appearance in the urine is noted. Normally, it appears in about thirty minutes. When delayed, renal "permeability" is supposed to be interfered with.
Thephloridzin testconsists in the hypodermic injection of a small quantity of phloridzin. This substance is transformed into glucose by the kidneys of healthy persons. In disease, this change is more or less interfered with, and the amount of glucose recoverable from the urine is taken as an index of the secretory power of the kidneys.
In applying these tests for "permeability," "secretory ability," etc., one must remember that the conditions are abnormal, and that there is no evidence that the kidneys will behave with the products of metabolism as they do with the substances selected for the tests, and also that the tests throw unusual work upon the kidneys, which in some cases may be harmful.
II. CHEMIC EXAMINATION
II. CHEMIC EXAMINATION
A. NORMALCONSTITUENTS
A. NORMALCONSTITUENTS
The most important are chlorids, phosphates, sulphates including indican, urea, and uric acid.
1.Chlorids.—These are derived from the food, and are mainly in the form of sodium chlorid. The amount excreted normally is 10 to 15 grams in twenty-four hours. It is much affected by the diet.
Excretion of chlorids is diminished in nephritis and in fevers, especially in pneumonia and inflammations leading to the formation of large exudates. In nephritis thekidneys are less permeable to the chlorids, and it is probable that the edema is due largely to an effort of the body to dilute the chlorids which have been retained. In fevers the diminution is due largely to decrease of food. In pneumonia chlorids are constantly very low, and in some cases are absent entirely. Following the crisis they are increased. In inflammations leading to formation of large exudates—e.g., pleurisy with effusion—chlorids are diminished, because a considerable amount becomes "locked up" in the exudate. During absorption chlorids are liberated and appear in the urine in excessive amounts.
Quantitative Estimation.—The best method for clinical purposes is the centrifugal method.
Purdy's Centrifugal Methods.—As shown by the late Dr. Purdy, the centrifuge offers an important means of making quantitative estimations of a number of substances in the urine. Results are easily and quickly obtained, and are probably accurate enough for all clinical purposes.
In general, the methods consist in precipitating the substance to be estimated in a graduated centrifuge tube, and applying a definite amount of centrifugal force for a definite length of time, after which the percentage of precipitate is read off upon the side of the tube. Albumin, if present, must be previously removed by boiling and filtering. Results are in terms ofbulk of precipitate, which must not be confused withpercentage by weight. The weight percentage can be found by referring to Purdy's tables, given later. In this, as in all quantitative urine work, percentages mean little in themselves; the actualamount eliminated in twenty-four hours should always be calculated.
The centrifuge should have an arm with radius of 6¾ inches when in motion, and should be capable of maintaining a speed of 1500 revolutions a minute. The electric centrifuge is to be recommended, although good work can be done with a water-power centrifuge, or, after a little practice, with the hand centrifuge. A speed indicator is desirable with electric and water-motor machines, although one can learn to estimate the speed by the musical note.
Estimation of Chlorids.—Fill the graduated tube to the 10 c.c. mark with urine; add 15 drops strong nitric acid and then silver nitrate solution (dram to the ounce) to the 15 c.c. mark. Mix by inverting several times. Let stand a few minutes for a precipitate to form, and then revolve in the centrifuge for three minutes at 1200 revolutions a minute. Each one-tenth cubic centimeter of precipitate equals 1 per cent. by bulk. The normal is about 10 per cent. This may be converted into terms of chlorin or sodium chlorid by means of the table upon page 60. Roughly speaking, the percentage of chlorin by weight is about one-twelfth the bulk-percentage.
2.Phosphates.—Phosphates are derived largely from the food, only a small proportion resulting from metabolism. The normal daily output of phosphoric acid is about 2.5 to 3.5 gm.
The urinary phosphates are of two kinds:alkaline, which make up two-thirds of the whole, and include thephosphates of sodium and potassium; andearthy, which constitute one-third, and include the phosphates of calcium and magnesium. Earthy phosphates are frequently thrown out of solution in neutral and alkaline urines, and as "amorphous phosphates" form a very common sediment. This sediment seldom indicates an excessive excretion of phosphates.
Quantitative estimationdoes not furnish much of definite clinical value. The centrifugal method is the most convenient.
Purdy's Centrifugal Method.—Take 10 c.c. urine in the graduated tube, add 2 c.c. of 50 per cent. acetic acid, and 3 c.c. of 5 per cent. uranium nitrate solution. Mix; let stand a few minutes, and revolve for three minutes at 1200 revolutions.The bulk of precipitate is normally about 8 per cent. The percentage of phosphoric acid by weight is, roughly, one-eighty-fifth of the bulk-percentage.
3.Sulphates.—The urinary sulphates are derived partly from the food, especially meats, and partly from body metabolism. The normal output of sulphuric acid is about 1.5 to 3 gm. daily.
Quantitative estimation of the total sulphates yields little of clinical value.
Purdy's Centrifugal Method.—Take 10 c.c. urine in the graduated tube and add barium chlorid solution to the 15 c.c. mark. This consists of barium chlorid, 4 parts; strong hydrochloric acid, 1 part; and distilled water, 16 parts. Mix; let stand a few minutes, and revolve for three minutes at 1200 revolutions a minute. The normal bulk of precipitate is about 0.8 per cent. The percentage by weight of sulphuric acid is about one-fourth of the bulk-percentage.
Nine-tenths of the sulphuric acid is in combination with various mineral substances (mineral or preformed sulphates). One-tenth is in combination with certain aromatic substances, mostly products of albuminous putrefaction in the intestine (conjugate sulphates). Among these aromatic substances are indol, phenol, and skatol. By far the most important of the conjugate sulphates and representative of the group is potassium indoxyl sulphate.
Potassium indoxyl sulphate, orindican, is derived from indol. Indol is absorbed and oxidized into indoxyl, which combines with potassium and sulphuric acid and is thus excreted. Under normal conditions the amount in the urine is small. It is increased by a meat diet.
Pathologically, an increase of indican always indicates abnormal albuminous putrefaction somewhere in the body. It is noted in:
(a)Diseases of the Small Intestine.—This is by far the most common source. Intestinal obstruction gives the largest amounts of indican. It is also much increased in intestinal indigestion—so-called "biliousness"; in inflammations, especially in cholera and typhoid fever; and in paralysis of peristalsis such as occurs in peritonitis. Simple constipation and diseases of thelargeintestine alone do not increase the amount of indican.
(b)Diseases of the stomachassociated with deficient hydrochloric acid, as chronic gastritis and gastric cancer. Diminished hydrochloric acid favors intestinal putrefaction.
(c)Decomposition of exudatesanywhere in the body, as in empyema, bronchiectasis, and large tuberculous cavities.
Detection of indicandepends upon its decomposition and oxidation of the indoxyl set free into indigo-blue.
Obermayer's Method.—In a test-tube take equal parts of the urine and Obermayer's reagent and add a small quantity of chloroform. Mix by inverting a few times; avoid shaking violently. If indican be present in excess, the chloroform, which sinks to the bottom, will assume an indigo-blue color. The depth of color indicates the comparative amount of indican if the same proportions of urine and reagents are always used. The indican in normal urine may give a faint blue by this method. Urine of patients taking iodids gives a reddish-violet color, which disappears upon addition of a few drops of strong sodium hyposulphite solution. Bile-pigments, which interfere with the test, must be removed (p. 48).
Obermayer's reagentconsists of strong hydrochloric acid (sp. gr., 1.19), 1000 parts, and ferric chlorid, 2 parts. This makes a yellow, fuming liquid which keeps well.
4.Urea.—From the standpoint of physiology urea is the most important constituent of the urine. It is the principal waste-product of metabolism, and constitutes about one-half of all the solids excreted—about 30 gm. in twenty-four hours. It represents 85 to 90 per cent. of the total nitrogen of the urine, and its quantitative estimation is a simple, though not very accurate, method of ascertaining the state of nitrogenous excretion. Normally, the amount is greatly influenced by exercise and diet.
Pathologically, urea is increased in fevers, in diabetes, and especially during resolution of pneumonia and absorption of large exudates. Other factors being equal, the amount of urea indicates the activity of metabolism. Inthis connection the relation between the amounts of urea and the chlorids is important. The amount of urea is normally about twice that of the chlorids. If the proportion is much increased above this, increased tissue destruction may be inferred, since other conditions which increase urea also increase chlorids.
Urea is decreased in diseases of the liver with destruction of liver substance. It may or may not be decreased in nephritis. In the early stages of chronic nephritis, when diagnosis is difficult, it is usually normal. In the late stages, when diagnosis is comparatively easy, it is decreased. Hence estimation of urea is of little help in the diagnosis of this disease, especially when, as is so frequently the case, a small quantity of urine taken at random is used. When, however, the diagnosis is established, estimations made at frequent intervals under the same conditions of diet and exercise are of much value,provided a sample of the mixed twenty-four-hour urine be used. A steady declineis a very bad prognostic sign, and a sudden marked diminution is usually a forerunner of uremia.
The presence of urea can be shown by allowing a few drops of the fluid to partially evaporate upon a slide, and adding a small drop of pure colorless nitric acid or saturated solution of oxalic acid. Crystals of urea nitrate or oxalate (Fig. 19) will soon appear and can be recognized with the microscope.
Quantitative Estimation.—The hypobromite method, which is generally used, depends upon the fact that urea is decomposed by sodium hypobromite with liberation of nitrogen. The amount of urea is calculated from the volume of nitrogen set free. The improved Doremus apparatus (Fig. 20) is the most convenient.
Pour some of the urine into the smaller tube of the apparatus, then open the stopcock and quickly close it so as to fill its lumen with urine. Rinse out the larger tube with water and fill it and the bulb with 25 per cent. caustic soda solution. Add to this 1 c.c. of bromin by means of a medicine-dropper and mix well. This prepares a fresh solution of sodium hypobromite with excess of caustic soda, which serves to absorb the carbon dioxid set free in the decomposition of urea. When handling bromin, keep an open vessel of ammonia near to neutralize the irritant fumes.
Pour the urine into the smaller tube, and then turn the stopcock so as to let as much urine as desired (usually 1 c.c.) run slowly into the hypobromite solution. When bubbles have ceased to rise, read off the height of the fluid in the largetube by the graduations upon its side. This gives the amount by weight of urea in the urine added, from which the amount excreted in twenty-four hours can easily be calculated. If the urine contains much more than the normal amount, it should be diluted.
To avoid handling pure bromin, which is disagreeable, Rice's solutions may be employed:
One part of each of these solutions and two parts of water are mixed and used for the test. The bromin solution must be kept in a tightly stoppered bottle or it will rapidly lose strength.
5.Uric Acid.—Uric acid is the most important of a group of substances, calledpurin bodies, which are derived chiefly from the nucleins of the food and from metabolic destruction of the nuclei of the body. The daily output of uric acid is about 0.4 to 1 gm. The amount of the other purin bodies together is about one-tenth that of uric acid. Excretion of these substances is greatly increased by a diet rich in nuclei, as sweetbreads and liver.
Uric acid exists in the urine in the form of urates, which in concentrated urines are readily thrown out of solution and constitute the familiar sediment of "amorphous urates." This, together with the fact that uric acid is frequently deposited as crystals, constitutes its chief interest to the practitioner. It is a very common error to consider these deposits as evidence of excessive excretion.
Pathologically, the greatest increase of uric acid occursin leukemia, where there is extensive destruction of leukocytes, and in diseases with active destruction of the liver and other organs rich in nuclei. Uric acid is decreased before an attack of gout and increased afterward, but its etiologic relation is still uncertain. An increase is also noted in the uric-acid diathesis and in diseases accompanied by respiratory insufficiency.
Quantitative Estimation.—The following are the best methods for ordinary clinical purposes, although no great accuracy can be claimed for them.
Cook's Method for Purin Bodies.—In a centrifuge tube take 10 c.c. urine and add about 1 gm. (about 1 c.c.) sodium carbonate and 1 or 2 c.c. strong ammonia. Shake until the soda is dissolved. The earthy phosphates will be precipitated. Centrifugalize thoroughly and pour off all the clear fluid into a graduated centrifuge tube. Add 2 c.c. ammonia and 2 c.c. ammoniated silver nitrate solution. Let stand a few minutes, and revolve in the centrifuge until the bulk of precipitateremains constant. Each one-tenth cubic centimeter of sediment represents 0.001176 gm. purin bodies. This amount may be regarded as uric acid, since this substance usually constitutes nine-tenths of the purin bodies and the clinical significance is the same.
Ammoniated silver nitrate solutionis prepared by dissolving 5 gm. of silver nitratein 100 c.c. distilled water, and adding ammonia until the solution clouds and again becomes clear.
Ruhemann's Method for Uric Acid.—The urine must be slightly acid. Fill Ruhemann's tube (Fig. 21) to the markSwith the indicator, carbon disulphid, and to the markJwith the reagent. The carbon disulphid will assume a violet color. Add the urine, a small quantity at a time, closing the tube with the glass stopper and shaking vigorously after each addition, until the disulphid loses every trace of its violet color and becomes pure white. This completes the test. The figure in the right-hand column of figures corresponding to the top of the fluid gives the amount of uric acid in parts per thousand. The presence of diacetic acid interferes with the test.
Ruhemann's reagentconsists of iodin and potassium iodid, each 1.5 parts; absolute alcohol, 15 parts; and distilled water, 185 parts.
B. ABNORMALCONSTITUENTS
B. ABNORMALCONSTITUENTS
Those substances which appear in the urine only in pathologic conditions are of much more interest to the clinician than are those which have just been discussed. Among them are: proteids, sugars, the acetone bodies, bile, hemoglobin, and the diazo substances. The "pancreatic reaction" and detection of drugs in the urine will also be discussed under this head.
1.Proteids.—Of the proteids which may appear in the urine, serum-albumin and serum-globulin are the most important. Mucin, albumose, and a few others are found occasionally, but are of less interest.
(1)Serum-albumin and Serum-globulin.—These two proteids constitute the so-called "urinary albumin." They usually occur together, have practically the samesignificance, and both respond to all the ordinary tests for "albumin."
Their presence, oralbuminuria, is probably the most important pathologic condition of the urine. It is eitheraccidentalorrenal. The physician can make no greater mistake than to regard all cases of albuminuria as indicating kidney disease.
Accidentalorfalse albuminuriais due to admixture with the urine of albuminous fluids, such as pus, blood, and vaginal discharge. The microscope will usually reveal its nature.
Renal albuminuriarefers to albumin which has passed from the blood into the urine through the walls of the kidney tubules or the glomeruli. It probably never occurs as a physiologic condition, the so-called "functional albuminuria" being due to obscure or slight pathologic changes.
Renal albuminuria may be referred to one or more of the following causes. In practically all cases it is accompanied by tube-casts.
(a)Changes in the bloodwhich render its albumin more diffusible, as in severe anemias, purpura, and scurvy. Here the albumin is small in amount.
(b)Changes in circulation in the kidney, either anemia or congestion, as in excessive exercise, chronic heart disease, and pressure upon the renal veins. The quantity of albumin is usually, but not always, small. Its presence is constant or temporary, according to the cause. Most of the causes, if continued, will produce organic changes in the kidney.
(c)Organic Changes in the Kidney.—These include the inflammatory and degenerative changes commonly groupedtogether under the name of nephritis, and also renal tuberculosis, neoplasms, and cloudy swelling due to irritation of toxins and drugs. The amount of albumin eliminated in these conditions varies from minute traces to 20 gm., or even more, in the twenty-four hours, and, except in acute processes, bears little relation to the severity of the disease. In acute and chronic parenchymatous nephritis the quantity is usually very large. In chronic interstitial nephritis it is small—frequently no more than a trace. It is small in cloudy swelling from toxins and drugs, and variable in renal tuberculosis and neoplasms. In amyloid disease of the kidney the quantity is usually small, and serum-globulin may be present in especially large proportion, or even alone. Roughly distinctive of serum-globulin is the appearance of an opalescent cloud when a few drops of the urine are dropped into a glass of distilled water.
Detection of albumindepends upon its coagulation by chemicals or heat. There are many tests, but none is entirely satisfactory, because other substances as well as albumin are precipitated. The most common source of error is mucin. The tests given here are widely used and can be recommended. They make no distinction between serum-albumin and serum-globulin. They are given as nearly as possible in order of their delicacy.
It is very important that urine to be tested for albumin be rendered clear by filtration or centrifugation. This is too often neglected in routine work. When ordinary methods do not suffice, it can usually be cleared by shaking up with a little magnesium carbonate and filtering.
(1)Trichloracetic Acid Test.—The reagent consists of a saturated aqueous solution of trichloracetic acid to whichmagnesium sulphate is added to saturation. A simple saturated solution of the acid may be used, but addition of magnesium sulphate favors precipitation of globulin, and by raising the specific gravity, makes the test easier to apply.
Take a few c.c. of the reagent in a test-tube or conical test glass, hold the tube or glass in an inclined position, and run the urine gently in by means of a pipet, so that it will form a layer on top of the reagent without mixing with it. If albumin be present, a white, cloudy ring will appear where the two fluids come in contact. The ring can be seen most clearly if viewed against a black background, and one side of the tube or conical glass may be painted black for this purpose.
This is an extremely sensitive test, but, unfortunately, both mucin and albumose respond to it; urates when abundant may give a confusing white ring, and the reagent iscomparatively expensive. It is not much used in routine work except as a control to the less sensitive tests.
A most convenient instrument for applying this or any of the contact tests is sold under the name of "horismascope" (Fig. 22).
(2)Robert's Test.—The reagent consists of pure nitric acid, 1 part, and saturated aqueous solution of magnesium sulphate, 5 parts. It is applied in the same way as the preceding test.
Albumin gives a white ring, which varies in density with the amount present. A similar white ring may be produced by albumose and resinous drugs. White rings or cloudiness in the urine above the zone of contact may result from excess of urates or mucus. Colored rings near the junction of the fluids may be produced by urinary pigments, bile, or indican.
Robert's test is one of the best for routine work, although the various rings are apt to be confusing to the inexperienced. It is more sensitive than Heller's test, of which it is a modification, and has the additional advantage that the reagent is not so corrosive.
(3)Purdy's Heat Test.—Take a test-tube two-thirds full of urine, add about one-sixth its volume of saturated solution of sodium chlorid and 5 to 10 drops of 50 per cent. acetic acid. Mix, and boil the upper inch. A white cloud in the heated portion shows the presence of albumin.
This is a valuable test for routine work. It is simple, sufficiently accurate for clinical purposes, and has practically no fallacies. Addition of the salt solution, by raising the specific gravity, prevents precipitation of mucin. Albumose may produce a white cloud which disappears upon boiling and reappears upon cooling.
(4)Heat and Nitric Acid Test.—This is one of the oldest of the albumin tests, and, if properly carried out, one of the best. Boil a small quantity of filtered urine in a test-tube and add about one-twentieth its volume of concentrated nitricacid. A white cloud or flocculent precipitate (which usually appears during the boiling, but if the quantity be very small only after addition of the acid) denotes the presence of albumin. A similar white precipitate, which disappears upon addition of the acid, is due to earthy phosphates. The acid should not be added before boiling, and the proper amount should always be used; otherwise, part of the albumin may fail to be precipitated or may be redissolved.
Quantitative Estimation.—The gravimetric, which is the most reliable method, is too elaborate for clinical work. Both Esbach's, which is very widely used, and the centrifugal method give fair results.
(1)Esbach's Method.—The urine must be clear, of acid reaction, and not concentrated. Always filter before testing, and, if necessary, add acetic acid and dilute with water. Esbach's tube (Fig. 23) is essentially a test-tube with a markUnear the middle, a markRnear the top, and graduations ½, 1, 2, 3, etc., near the bottom. Fill the tube to the markUwith urine and to the markRwith the reagent. Close with a rubber stopper, invert slowly several times, and set aside in a cool place. At the end of twenty-four hours read off the height of the precipitate. This gives the amount of albumin ingrams per liter, and must be divided by 10 to obtain the percentage.
Esbach's reagentconsists of picric acid, 1 gm., citric acid, 2 gm., and distilled water, to make 100 c.c.
(2)Purdy's Centrifugal Method.—This is detailed in the accompanying table. The percentage by weight is approximately one-fiftieth of the bulk percentage.