In Pyaemia and Ulcerative endocarditis pieces of fibrine or other material may be carried to the kidneys and produce embolism there. In this way arise Metastatic abscesses. For the most part the emboli are small and are carried to the ascending arteries or the glomeruli before they are caught. Hence the abscesses are mostly in the cortical substance, although they are not infrequently seen in the pyramids along the course of the arterise rectse, and there may even be large ones taking in portions both of pyramids and cortex. The abscesses are usually elongated in the direction of the arteries, and they often project slightly from the surface when the capsule is removed. They are frequently present in considerable numbers in both kidneys.

Under the microscope it can be seen that the abscesses arise by obstruction of the arteries (see Fig. 431). Where the embolism has been recent the wall of the vessel and the tissue in the immediate neighbourhood of the embolus present evidences of necrosis, while around there are multitudes of leucocytes occupying the interstitial tissue. In the embolus there are colonies of microbes, in the midst of remains of the transported fibrine. When the abscess has fully formed, these characters may be lost in the great multiplication of leucocytes. Besides in the arteries colonies of microbes are to be found in the vessels of the glomeruli, sometimes filling many of them out with a dark granular mass, and also in the capillaries. It is sometimes to be seen that these colonies are present in the glomeruli and capillaries without signs of inflammation around. In such cases they are of recent growth and have not had time to produce inflammation by giving off irritating products. To some extent the bacteria may multiply in the glomeruli and capillaries after death.

Fig. 481. - From a section of the kidney in ulcerative endocarditis. An artery is plugged with dark material which contains micrococci. In the neighbourhood of the plug the wall of the artery is necrosed. Leucocytes are infiltrating the tissue around, and extending through the vessel wall, x 90.

In scarlet fever there is rarely a true suppurative nephritis, but in some cases the kidneys are greatly enlarged and infiltrated with leucocytes. These cases are probably due to the presence of septic products, absorbed from the lesion in the fauces. Microbes are not infrequently found in the capillaries of the kidney in scarlet fever and diphtheria, and they may also pass into the tubules.

Fig. 482. - Bacteria distending a capillary blood-vessel in a case of scarlet fever, x 850.