Hydro-nephrosis, in the entire absence of inflammatory symptoms and in the presence of conditions likely to cause it known to exist in the lower urinary passages, may be rather suspected than diagnosticated until the appearance of a tumor. Some dull pain in the loins without irradiations in any direction may exist, but so common a symptom can have but little weight in diagnosis. For an early recognition of swelling in suspected cases where nothing can be felt anteriorly, it has been recommended that the patient be placed upon the hands and knees, when the flank upon the affected side, instead of falling slightly forward and leaving a shallow depression outside of the erector spinæ, will remain full or protuberant. When an enlargement evidently connected with the kidney makes its appearance after obstruction to the passage of urine is known to exist, the diagnosis may often be very simple; but if the tumor be the first phenomenon observed, as may easily happen when the obstruction is situated high up or even at the commencement of the ureter, it may require to be distinguished from several other kinds of tumor occupying the lumbar region, or, since hydro-nephrosis of a movable or misplaced kidney sometimes takes place, from tumors of the abdomen in general. From solid malignant tumors of the kidney the feeling of comparative elasticity and fluctuation will in most cases distinguish it, though an encephaloid kidney may be so soft as to render the second of these points of {59} comparatively little value. Absence of hæmaturia and of the cancerous cachexia, though not conclusive, would have much weight. A hydatid cyst might counterfeit a hydro-nephrosis, but instances of this affection having its primary seat in the kidney are of extreme rarity. An ordinary cystic kidney is most likely to be connected with chronic diffuse interstitial nephritis, which will have made itself manifest by the usual symptoms, and is moreover unlikely to attain the dimensions of a large or even moderate hydro-nephrosis. In a thin person the ureter might, if felt dilated through the abdominal walls, clear up the diagnosis. Extreme cases of cystic kidney with comparatively little nephritis may, however, present great similarity and cause difficulty in diagnosis. From most other tumors of the abdominal cavity those of the kidney present the important distinction that they are situated behind the peritoneum, and consequently behind the intestines, so that the surface of a renal tumor is likely to be crossed by a more or less extensive area of percussion resonance, representing usually the large intestine. This criterion is, however, not absolute, since a renal tumor may push the colon completely to one side, or, on the other hand, tumors not connected with the kidney may allow the intestine to come between themselves and the abdominal wall.