It is especially in surgical affections of the urinary passages, involving, as many of them do, considerable obstruction with a more or less intense cystitis, that we meet with the combination of the two conditions. Such are enlarged prostate with its usual obstruction and frequent chronically-distended bladder, with ammoniacal, purulent, and decomposing urine, or stricture with frequent over-contraction of the bladder, forcing the urine backward as well as forward. In diseases of the female generative organs we are more likely to have the hydro-nephrosis and pyelitis as separate affections, since the compression which so frequently arises in cases of cancer or of pelvic inflammation is likely to be above the bladder, thus preventing the regurgitation of urine as well as its passage downward. Two conditions of the renal substance seem to result from pyelitis of this kind: one, a chronic nephritis already described, with increased formation of connective tissue, atrophy of the tubes and the Malpighian bodies (the latter, however, remaining recognizable, although crowded together), and a general, and at times extreme, shrinking of the whole organ. The other is more acute, and consists in the formation of abscesses of small size, which in the medullary portion are somewhat elongated and arranged parallel to the tubes, and in the cortical portion preserve a less degree of regularity, though still having some reference to the columnar arrangement of the masses of convoluted tubes. The intervening structure is usually in a marked condition of parenchymatous degeneration. This is the so-called surgical kidney. Whether the one or the other of these processes shall take place probably depends chiefly on the infectiousness of the cystitis or of the urine {54} contained in the bladder and backing up into the kidneys, although it is not necessary that any degree of dilatation should be present for this condition to arise. Sometimes also the surgical kidney may be found when the original cystitis is not at all severe. The DIAGNOSIS of a pyelitis supervening on a cystitis is not always easy, but may frequently be inferred, and it is possible that by careful treatment of the cystitis it may be reduced to a very low grade of severity, while the pyelitis still remains, which will permit the diagnosis to be somewhat more conclusive.