The procedure recommended by Thompson may be resorted to in order to determine whether the urine comes from the kidneys loaded with cellular detritus, or whether the addition is made in the bladder. This consists in washing out thoroughly the bladder with several successive quantities of water through a single catheter, until the water comes away clear and the bladder has contracted itself around the instrument, when the urine from the kidneys will for a time come through direct and comparatively uncontaminated. In cases where the urine is alkaline in the kidney, which may happen, distinctions founded on the reaction cannot be of value, and the same {50} may be said of cases where cystitis is known to exist, but where there is in addition a possibility of a renal calculus. In these some such mechanical procedure as that just described must be resorted to. The presence of a calculus as a cause of pyelitis cannot always be demonstrated, but may be more or less strongly suspected according to the conclusiveness with which any other cause can be excluded, by the definiteness and character of the local pain, the history of renal colic, the presence of uric-acid crystals in the urine, and perhaps in some cases the results of palpation. The exploring-needle may be used, and may of course, if reaching the calculus and giving a characteristic grating feeling and sound, give absolutely positive results; but a failure to strike a stone could hardly be regarded as proof positive of its absence. The diagnosis of renal calculus from lumbago or neuralgia should rest, in case the pain is severe enough or long-continued enough to really cause the question to arise, upon an examination of the urine.