Pyuria indicates suppuration in some part of the urinary {124} tract--urethritis, cystitis, pyelitis, etc.--or may be due to contamination from the vagina, in which case many vaginal epithelial cells will also be present. In general, the source of the pus can be determined only by the accompanying structures (epithelia, casts) or by the clinical signs. A fairly accurate idea of the quantity of pus from day to day may be had by shaking the urine thoroughly and counting the number of corpuscles per cubic millimeter upon the Thoma-Zeiss blood-counting slide. [Illustration: FIG. 51.--Pus-corpuscles: _a_, As ordinarily seen; _b_, ameboid corpuscles; _c_, showing the action of acetic acid (Ogden).] 4. Red Blood-corpuscles.--Urine which contains blood is always albuminous. Very small amounts do not alter its macroscopic appearance. Larger amounts alter it considerably. Blood from the kidneys is generally intimately mixed with the urine and gives it a hazy reddish or brown color. When from the lower urinary tract, it is not so intimately mixed, and settles more quickly to the bottom, the color is brighter, and small clots are often present. Red blood-corpuscles are not usually difficult to recognize with the microscope. When very fresh, they have a normal appearance, being yellowish discs of uniform size (normal blood). When they have been in the urine any {125} considerable time, their hemoglobin may be dissolved out, and they then appear as faint colorless circles or "shadow cells" (abnormal blood), and are more difficult to see (Fig. 52; see also Figs. 45 and 60). They are apt to be swollen in dilute and crenated in concentrated urines. The microscopic findings may be corroborated by chemic tests for hemoglobin, although the microscope may show a few red corpuscles when the chemic tests are negative. [Illustration: FIG. 52.--Blood-corpuscles: _a_, Normal; _b_, abnormal (Ogden).] When not due to contamination from menstrual discharge, blood in the urine, or _hematuria_, is always pathologic. Blood comes from the kidney tubules in severe hyperemia, in some forms of nephritis, and in renal tuberculosis and malignant disease. The finding of blood-casts is the only certain means of diagnosing the kidney as its source. Blood comes from the pelvis of the kidney in renal calculus (Fig. 62), and is then usually intermittent, small in amount, and accompanied by a little pus and perhaps crystals of the substance forming the stone. Considerable hemorrhages from the bladder may occur in vesical calculus, tuberculosis, and newgrowths. Small amounts of blood generally accompany acute cystitis. 5. Spermatozoa are generally present in the urine of men after nocturnal emissions, after epileptic convulsions, and in spermatorrhea. They may be found in the urine of both sexes following coitus. They are easily recognized {126} from their characteristic structure (Fig. 53). The one-sixth objective should be used, with subdued light and careful focusing.