In the stroma, especially in the cortex, there is a new growth of connective tissue. This new connective tissue is in patches of varying size, surrounds Malpighian bodies and blood-vessels, and may be continuous with the capsule of the kidneys.
The arteries are frequently changed. There is a general thickening of all their coats, usually a simple sclerotic thickening.
All these changes, when they have once begun in the kidneys, have a natural tendency to go on and become more and more marked. There is much difference in different kidneys in the predominance of one or more of these changes over others. In one kidney the changes in the tubes will be most marked, in another those in the Malpighian bodies, in another those in the stroma. But there seems no good reason for believing that these changes are developed successively—that there is first a lesion of the stroma, then a lesion of the tubes, or first a lesion of the tubes, and then of the stroma. The earliest examples of chronic diffuse nephritis, obtained from persons dying accidentally of other diseases, show that the lesions are diffuse at the very outset.
In the atrophied kidneys the new connective tissue is in patches. In the earliest stages of the lesion these patches are confined to the region close to the capsule; later in the disease the whole thickness of the cortex is involved. The tubes embraced within these areas of new connective tissue are atrophied and collapsed. The rest of the cortex-tubes exhibit marked degenerative changes in the epithelium, and often cast-matter. Dilatation of the tubes is very common. The Malpighian bodies are usually much altered—the capsules thickened, the tufts atrophied. Occasionally there is waxy degeneration of the Malpighian tufts. There are some atrophied kidneys in which the changes in the stroma are very slight.
In the large white kidneys there is much variety. In some of them one is surprised to find how slight the minute lesions are. In others the principal changes are in the epithelium of the tubes, so that it may be difficult to tell whether they are examples of parenchymatous or of diffuse nephritis. In many others there is a very marked production of new connective tissue either in patches or diffuse. The large white kidneys which are waxy differ from the others only in the addition of the waxy degeneration of the Malpighian tufts and arteries to the other lesions. I have no knowledge of any kidneys in which waxy degeneration exists without the presence of the regular lesions of diffuse nephritis.
In the large white kidneys of cardiac disease the large thickened arteries are a prominent feature.
ETIOLOGY.—Chronic diffuse nephritis is more common in males than in females. It is said to occur at nearly all ages; the maximum liability is in persons between the ages of forty-five and fifty-five years. The disease prevails principally in temperate climates; in New York it is of very common occurrence. Persons who are habitually intemperate, who have constitutional syphilis, who suffer from privation, are very liable to the disease. There is a disposition in certain families to the development of the disease. Not that it is, strictly speaking, hereditary, but there will be a number of examples of it in the same family. A number of brothers and sisters or of more distant relatives in the same family will at different times suffer from the disease. There seems also to be some sort of relationship between chronic diffuse nephritis and pulmonary phthisis. Not only does nephritis complicate phthisis, but in the same family some members have phthisis, others nephritis.
Acute diffuse nephritis and chronic congestion of the kidney may be followed by chronic diffuse nephritis.
Heart disease, emphysema, phthisis, cirrhosis of the liver, chronic inflammation of the bones and joints, gout, rheumatism, and chronic arteritis, are often complicated by the disease.