Two very interesting forms of Deposition in the tubules are met with in new-born children. In the common icterus of the new-born the Biliary colouring matter (bilirubin) is excreted, as in the adult, by the kidneys, but in the new-born it very readily passes into the Crystalline form, so that round or rhombic orange-coloured crystals are found in the pyramidal tubules, sometimes in such numbers as to warrant the designation bilirubin-infarction. Similar crystals are found in the blood and tissues of the body.

Uric acid salts are found in the tubules of new-born children, in about half the cases of those who die within the first few weeks. It is mostly in children who have breathed that they are met with, but they have been observed in still-born children, although very rarely. The concretions consist mostly of urate of ammonia. They are deposited mainly in the tubules near the apices of the pyramids, giving the appearance of opaque yellow or reddish streaks, converging to the apex of the pyramid. Under the microscope amorphous urates are seen in the tubules, and when acetic acid is applied these dissolve and form crystals of uric acid.

Fig. 437. - Cloudy swelling of renal epithelium. The cellsare enlarged and filled with finegranules, in addition to which there are occasional minute oil drops, x 350.

In adults, icterus is also accompanied by deposition of pigment in the tubules, but it is in the form of brown or yellowish masses.

Urates are also deposited in the substance of the kidney in Gont. They are visible to the naked eye in the pyramidal portions of the kidney, especially towards the apices, as white streaks. With the microscope they are seen to occupy the tubules, which are dilated. There is usually a co-existing interstitial nephritis.

Lime salts are sometimes deposited in the straight tubules of the pyramids, especially in cases where from disease of bone there is excessive absorption of lime salts and excretion of them by the urine. The appearance presented is that of white streaks usually near the apices of the pyramids. It is to be observed, however, that a deposition of urates occurring in the straight tubules after death may produce a somewhat similar appearance.

Calculi in the pelvis of the kidney are of frequent occurrence. As we have seen, they may originate from chronic pyelitis, especially with stagnation of urine, but they may apparently originate in the uriniferous tubules, and having passed into the pelvis grow larger there. The calculi may be composed of uric acid, of phosphates, of oxalate of lime, or of cystine. The character of each of these is described in the section on Calculi in the Bladder.

The calculi sometimes attain to very large dimensions, moulding themselves into the shape of the pelvis and calices, so that we may have branches extending out into elongated recesses formed by dilated calices. By obstructing the flow of urine these calculi may lead to the occurrence of hydronephrosis, and as the cavity of the pelvis and calices enlarges so may the calculus. A small calculus often passes into the ureter and obstructs it, in this way leading to hydronephrosis.