Experiments with various toxics, and clinical facts show that the pathological process is a uniform one, the epithelium of the convoluted tubules, the epithelial cells of the straight tubules, the glome ruli, the interstitial tissue, and vascular walls being, in turn, involved. Bur meister (Virchow's Archiv, B. 137, II. 3).
4. Pregnancy may act as a cause of acute nephritis (gravidarum). In such cases it usually appears in primiparu, in the last months of gestation, and is ably the result of renal engorgement due both to mechanical pressure and to nutritive disturbances in the kidney, owing to the altered blood-condition.
5. Latent chronic nephritis may form the cause of a manifest acute nephritis. Pathology.—There is a considerable variation in the anatomical changes in and the appearance of the kidneys, ac cording to the degree of involvement. Between the very mild and grave cases there is an intermediate series of tinuously more marked pathological changes dependent upon the amount of poisonous material circulating in and eliminated by the kidneys, as well as upon the intensity and duration of its toxic action.
There may be no microscopical change in the mildest cases. As a rule, how ever, the kidneys are slightly enlarged, swelled, and somewhat softened, though these conditions are more evident when the interstitial exudation is abundant and inflammatory oedema is evident. On section the organs may appear red and congested or they may be pale and mottled. In the former case haemor rhages may appear beneath the capsule (acute hwmorrhagic nephritis); it is more usual, however, to see red, hyper vemic patches alternating with opaque and whitish portions, both on the outer and the cut surfaces. Especially is the cortex swelled, turbid, and pale, or slightly congested in the mildest cases; in severe attacks it is deeply mottled (red and pale glomeruli) or hyperemic. The surfaces are smooth and the capsule non-adherent. The pyramids usually show an intense-red color.
In the very mild cases, already referred to, changes may be noted microscopic ally that are not visible to the naked eye, there being simply a cloudy swelling or a granular (parenchymatous) degen eration of the epithelium of the Mal pighian tufts, Bowman's capsule, and of the uriniferous tubules of the cortex.
In the absence of exudative changes in the interstitial tissue, however, this can not be called true acute nephritis. The acute parenchymatous degeneration may be limited almost exclusively to the glomeruli, as in some cases of scarlatina, and from this fact has arisen the term "glomerulonephritis." The muscles are either swollen or absent; the cells are swollen, opaque, and irregular in shape; and the cell-contents are granular (albu minoid or fatty). The death of the cells—owing to coagulation necrosis or disintegration, desquamation, and hya line degeneration of masses of the cells in the tubules—marks a further stage in the process. Acute degenerative changes are frequently found in the acute infec tious diseases, or when inorganic poisons have been introduced into the body. In phosphoric poisoning there may be an actual fatty degeneration of the epithe lium, either proceeding from the cloudy swelling or occurring as an independent development. In severe cases a rapid necrosis of the cells is also met with.
True acute nephritis exhibits not only changes in the parenchyma (epithelium), but also an inflammatory exudate be tween the tubules, consisting of serum, leucocytes, and red blood-corpuscles. In some places the kidneys show only a slight cellular infiltration of the inter tubular tissues. In others the intersti tial tissue is swelled by the coagulated serofibrinous exudate, many leucocytes, and some erythrocytes, besides the des quamation of necrotic epithelial cells and the presence of hyaline casts in the tubules. The inflammatory exudate col lects, also, in the Malpighian bodies and tubules. The tubules may be dilated and choked with degenerated cells, or more frequently the straight tubules are clogged with hyaline casts. The lining epithelium, especially in the convoluted portion of the tubules, is often flattened. The white blood-corpuscles infiltrating the stroma of the kidneys are collected in foci in the cortex, and not, as a rule, equally diffused.