3. The phloridzin test is one of the most trustworthy for estimating the secretory function of the kidneys, as it shows how much active working epithelium remains in the organ. It consists in the subcutaneous injection of 0.005 Cc. sterilized phloridzin with an equal quantity of sodium benzoate, to hold the former in solution. The bladder must be emptied just before the injection is given. About an hour after its administration sugar should appear in the urine, if the kidneys are acting normally. If they are to be studied separately, catheterization of the ureters is necessary. The test is, of course, worthless in diabetic subjects. It depends upon the amount of sugar excreted, the time of its appearance, and the duration of its elimination. If no sugar be present the kidneys are seriously affected; if it be delayed, renal insufficiency is present. The average quantity of sugar eliminated during the first half-hour, when the kidneys are normal, is about 0.5 per cent. If the kidneys be diseased, this quantity is reduced by a half, and there is very little more secreted in the first than during the second half-hour. This valuable method is unfortunately difficult of application and requires minutely careful chemical tests.
4. Chromocystoscopy, introduced by Voelcker and Joseph, is perhaps the simplest of all methods of estimating renal capacity. 20 Cc. of a 0.4 per cent. solution of indigo-carmine is injected into the gluteal muscles. In fifteen or twenty minutes, if the kidneys be normal, the cystoscope will reveal dark-blue urine flowing from the ureteral orifices toward the median line, with a peculiar jet at regular intervals of about twenty-five seconds, and lasting for perhaps five seconds. There is both rhythm and force about this ejaculation. If the color be pale, the jet weak, or the rhythm irregular, the intervals prolonged or late, or if no flow whatever occur, there must be hindrance in the secreting and filtering structure of the kidney, or occlusion of the ureter. The results given by indigo-carmine in these cases are superior to those furnished by methylene blue, since it is not so much a solution as a mixture which is formed and ejaculated as such. Moreover, in passing through the body the indigo-carmine undergoes no reduction. By this method there is no necessity for catheterization of the ureter. One needs only to use the cystoscope with reasonable dexterity, and there is no necessity for chemical tests of separate specimens. The method is generally useful in cases where ureteral catheterization is made impossible by growths. It affords an easy means of differentiation, for instance, between ovarian cyst and hydronephrosis.
5. The toxin test is one only to be carried out by the use of animals, since it depends upon the amount of filtered urine required to kill an animal after injection into its veins, the number of cubic centimeters necessary to kill, divided by the weight of the animal, being called the urotoxic co-efficient. It has greater laboratory than clinical interest.
6. Electroconductivity of urine is of value in determining the capacity of the kidney for eliminating inorganic cells. It depends on the resistance offered by the urine to the electric current. It is complicated in method, requires special apparatus, and its results are still of questionable value.
For ordinary purposes the most trustworthy data for the surgeon who is not provided with ample laboratory facilities are afforded by an estimate of the amount passed in twenty-four hours, its specific gravity, its color and acidity, and by the presence or absence of albumin. The test-tube and the microscope then still afford satisfactory means of deciding those matters which the surgeon needs to know. If applied to urine collected separately from each kidney, they may be regarded as trustworthy. If catheterization be impossible, then it is advisable to inspect the ureteral orifices while elimination of indigo-carmine is taking place.
Hematuria.
—The significance of blood in the urine is rather that of a symptom than of a disease, although it should be admitted that there are occasional patients who lose blood in this way, more or less frequently, even periodically, without seeming to suffer in the least. Hematuria may also be present as an expression of vicarious menstruation. Again, blood may thus appear in scurvy and similar conditions, especially in tropical climates; in certain of the domestic animals its presence may be due to infection of the kidneys by macroscopic parasites (the so-called “black-water fever” of men and horses). Such cases as these are outside the pale of surgery. Nevertheless general experience has shown that many cases of hematuria, without perceptible changes in the kidney, have been benefited or cured by exploratory nephrotomy. Among the causes ascribed for these so-called “essential hematurias” have been incipient tuberculosis, renal retention from prostatic enlargement, congestion from venous obstruction (due to tight lacing or displacement from any cause), and even the congestion of chronic nephritis.
Treatment.
—When known or recognizable causes are absent, and the ordinary therapeutic agents, the special styptics (cotarnin), and such measures as hypodermoclysis with a 2 per cent. gelatin solution (see [Control of Hemorrhage]) have failed, an exploration may be advised. It is of the greatest advantage to be certain that but one kidney is involved, or it may be necessary later to operate on the second kidney.