The cortical portion is composed of bundles of straight tubes and of convoluted tubes and glomeruli, alternating with each other. The stroma is delicate and scanty in the cortex, firmer and more abun dant in the pyramids. In most adult kidneys there are little areas of connective tissue scattered in the cortex close under the capsules. The lymphatics are numerous, and consist of a superficial and a deep set.
It is the function of the kidneys to remove from the body fluid and excrementitious substances. It is generally believed that the fluid is discharged by the glomeruli, and the excrementitious substances separated from the blood by the epithelium of the cortex tubes.
It is evident that for the proper performance of the functions of the kidneys there must be : (1) A free supply of blood to the kidney, a free circulation of blood through it, and an easy escape of blood through the renal vein. Any obstruction to the flow of blood, any changes in the tufts of the glomeruli, and any obliteration of the capillaries interfere with the fulictions of the kidneys. (2) The blood supplied to the kidney must be of normal composition; other wise there will be a change in the character and quantity of the substances excreted. (3) The uriniferous tubules must be of normal size and unobstructed. The epithelial cells which line them must be healthy.
The study of the diseases of the kidney is, therefore, a study of the changes in the circulation of the blood in these organs, of the composi tion of the blood which is supplied to them, and of anatomical changes affecting the tubes, the stroma, the glomeruli and the blood-vessels.
Classification of Diseases of the Kidney.
The recognition of the diseases of the kidney, which still bear the name of their discoverer, dates back only to the year 1827, when Richard Bright published his first paper on the subject. This first paper was followed by others, and in 1829 Christison published in the Edinburgh Medical and Surgical Review his account of the same dis ease. Both these authors regarded the disease as a morbid change in the kidneys, which was the cause of the accompanying symptoms.
In 1841 Rayer completed his large atlas of colored plates and de scription of kidney diseases. His classification is as follows :
1. Nephritis—an inflammation of the cortical or tubular portion of the kidneys : (a) Simple nephritis ; (5) Gouty nephritis ; (c) Rheumatic nephritis ; (d) Nephritis produced by poison; (e) Albu minous nephritis ; 2. Pyelitis ;• 3. Perinephritis.
In 1842 Rokitansky recognized the waxy, or amyloid, kidneys as presenting different lesions from those found in other examples of kidney disease.
In 1851 Frerichs published his monograph on Bright's disease, and gave a systematic description which has had a decided effect on the minds of most subsequent observers. His conception is that of one disease—Bright's disease, with a characteristic lesion—inflam mation of the kidneys. The varieties of the disease depend upon the stages of the inflammation. There are three stages : 1. The stage of hyperemia and of commencing exudation.
2. The stage of exudation and of commencing transformation of the exudation.
3. The stage of atrophy.
1. Hypercernia. —The first stage is characterized by an increase in the size of the kidneys, especially of the cortex, by general congestion, by extravasations of blood in the Malpighian bodies, the tubes, and the kidney tissue, and by filling of the tubes with coagulated fibrin. The epithelium of the tubes is unaltered.
2. Exuclation.—In the second stage, the congestion diminishes while the exudation increases. The exudation is found in the tubules and in the interstitial tissue. The exudation between the tubes is sometimes organized into connective tissue. The cortex becomes of a white-yellowish color, and remains thickened. The surface of the kidney is smooth or slightly granular. The pyramids are of a red dish color. Some of the Malpighian bodies are normal, others are enlarged and filled with exudation. In the cortex the epithelium of the tubes is swollen and granular, and may break clown altogether, or it simply shrivels and atrophies. The tubes are filled with degener ated epithelium, granular matter, and fat-globules, or with homoge neous exudation. The tubes are dilated. The dilatation of the tubes is the principal or only cause of the increased size of the kidney.