Active congestion, not easily distinguished from early acute in flammation, is produced by excretion in the urine of such materials as alcohol, turpentine, cantharides and the toxins of various diseases. Extreme congestion may follow exposure to cold, owing to the intimate relationship existing between the cutaneous and the renal vessels. Most acute specific diseases produce during their height a temporary nephritis, not usually followed by per manent alteration in the kidney; but some acute diseases cause a nephritis which may lay the foundation of permanent renal disease. This is most common as a result of scarlet fever.
is the term (q.v.) loosely applied to certain varieties of kidney affection. Three forms are usually recognized—acute, chronic and the granular or fibrotic kidney. Of these, acute Bright's disease (acute nephritis) has been dealt with elsewhere. Chronic Bright's disease (chronic nephritis) is sometimes the sequel of the acute form, but often the malady is chronic (or, rather, sub-acute) from the beginning. Both acute and chronic nephritis are inflammatory. Acute and chronic changes often co-exist in the same kidney because of recrudescences and remissions of the renal disease. An example will make this point clear. Assume that a person has (I) acute nephritis in the course of scarlet fever, (2) convalesces, (3) is exposed to cold six months later, (4) recovers again, and (5) is again exposed to cold. His kidneys show acute inflammatory changes due to (5), somewhat chronic changes due to (4), very chronic changes due to (2), and remnants of acute changes due to (I) and (3). Since all the acute changes lead to swelling of the organ and the chronic changes lead to contraction according to the degree of chronicity, it follows that such a kidney may be larger or smaller than, or the same size as, a normal kidney ; that its naked eye appearance may be greatly or little changed but, assuredly, that its microscopical texture will be profoundly altered. A granular kidney is not in flammatory in the usual sense of the term but, by reason of its abnormality, is liable to undergo inflammation. In this case acute nephritic changes are superposed on those characteristic of granu lar kidney, and a condition arises that may be mistaken for that occurring in the hypothetical case above.
In Bright's disease all the renal elements, glomeruli, tubular epithelium, interstitial tissue with its contained blood-vessels, are affected, though in differing degrees. In acute scarlatinal nephritis the most obvious changes are in the glomeruli ; in acute nephritis due to exposure the blood-vessels are congested to such an extent that the capsule of the kidney may be ruptured and the tubular epithelium is profoundly changed ; in granular kidney the primary change concerns the connective tissue framework and tubules and glomeruli are affected secondarily. Granular kidney, indeed, is a
specialized part of a general condition affecting the arterial system and left side of the heart (arterio-sclerosis). Whether as a result of glomerular or tubal changes, or both combined, the character of the urine is changed. Blockage of the tubules by desquamated epithelium leads to diminution in amount of urine, and the dam aged glomeruli and tubules allow albumen and blood to pass through their walls to become mixed with the urine, while "casts" of the tubules composed of epithelial or coagulated albuminous cylinders make their appearance. Such changes are to some degree a measure of the damage the kidney has undergone. In uncompli cated granular kidney with the associated high arterial tension the urine is increased in amount, of low specific gravity, contains no more than a trace of albumen and at most a few hyaline casts. The causes of acute, subacute and chronic nephritis are those given above for acute congestion, with the addition of pregnancy. Chronic lead poisoning and gout are undoubtedly associated with granular kidney in some cases, but in the majority no other cause than that of arterio-sclerosis can be inculpated.
The kidney may be infected by tubercle in two ways : ascending, in which the primary lesion is in the testicle, epididymis, or urinary bladder, the lesion travelling up by the ureter or the lymphatics to the kidney ; descending, where the tubercle bacillus reaches the kidney through the blood-vessels. In the latter case, miliary tubercles, as scattered granules, are seen, especially in the cortex of the kidney; the lesion is likely to be bilateral. In primary and in ascending tuberculosis the lesion is at first unilateral. In an advanced case the pelvis of the kidney is filled with caseous material, and caseous foci breaking down in the centre are scattered through the solid part of the organ. New Growths.—Malignant disease of the kidney takes the form of sarcoma or carcinoma. Sometimes it is a hypernephroma, starting in what are spoken of as "adrenal rests" in the cortex of the kidney. The kidney is not so prone to malignant disease as other organs, such as the stomach, bowel or liver.