The same circumstances that give rise to deposits or metastases in the lungs, the liver, and the spleen, may induce them in the kidneys. They follow inflammations of the endocardium, and of the lining membrane of the vessels brought on by infection of the blood, arising from absorption of the inflammatory product, or they result from suppuration and gangrene of membranous and parenchymatous tissues produced in a similar manner, or lastly they originate in spontaneous pyaemia. We would again direct especial attention to the deposits arising from endocarditis, as they have not only been overlooked, in the same way as those occurring in the spleen have been, by the most distinguished inquirers, but as of late Rayer has interpreted them falsely, and has viewed them as symptoms of rheumatic nephritis.

They are found in endocarditis, generally coexistent with similar deposits in the spleen, consequent upon primary phlebitis with a purulent exudation, or upon the absorption of pus or sanious matter from ulcerating surfaces or abscesses; they co-exist with deposits in the lungs, the liver, the brain, the subcutaneous, and intermuscular cellular tissue, the interstitial cellular layers of the intestines, and with secondary phlebitis, in the most different portions of the venous system.

There may be only a few, and in endocarditis we generally find one only, or they are as under the last-named conditions, very numerous; in rare cases the kidney is entirely gorged with them.

They occur chiefly in the cortical substance, and here again mainly in its peripheral strata; so that they are at once apparent on the removal of the fascia albuginea; it is only in exceptional cases, and when they are very numerous, that they occur in the pyramids. They vary much in size, from that of an almost imperceptible poppy-seed, to that of a millet- or hemp-seed, of a pea, a bean, or of a walnut; the larger ones present the peculiar form described in the section on the spleen, as exhibiting a pyramidal shape, the base of which is directed towards the surface, the apex towards the interior of the organ; the smaller ones appear as rounded nodules. The intermediate sizes are the most frequent, but when very numerous, they generally remain so small as scarcely to exceed the size of millet-seeds.

They commence in the renal parenchyma as dark-red indurated spots, which correspond in extent to the above-mentioned sizes; they gradually assume a dirty brown, yellow, or yellowish-white color, and are surrounded by a light-red inflammatory halo, which indicates the reaction set up in the adjoining tissue, or if the disorganization advances to a high degree, by a dark-red, discolored ecchymosis. The latter appearance is coincident with a very large number of the deposits, and as we have seen that these must then be very small, we find the renal tissue presenting in the advanced stage of the disease very numerous small red spots, in the centre of which an almost imperceptible yellowish-white spot is discovered.

The further progress of the disease consists in a conversion of the deposit into a purulent or sanious fluid, and the abscess may be enlarged by an analogous transformation of the inflammatory halo; the metamorphosis may, however, be benignant, and the deposit become pale, and shrivel up; it may then, together with the involved tissues, be absorbed, or partially retained as a pulpy or cretaceous mass, having a cicatriform cavity with a fibro-cellular investment, or a fibro-cellular callus, which corrugates and draws down the surrounding parts; a greasy yellow substance or chalky concretion is found buried in the callus, and like the investment of the first-mentioned cavity, this is agglutinated to the tunica albuginea.

The deposit is essentially an exudative process, the product of which undergoes the described metamorphoses; or it depends upon stasis and coagulation of the blood in the capillary vessels, and a conversion of the fibrine in the manner above described, - a secondary angioitis (phlebitis) capillaris. Both metamorphoses are known to be induced by something that is taken up by the blood; and we thus generally see deposits in the kidneys resulting from endocarditis, which go through the second metamorphosis, and heal with loss of substance of a small section of the cortical tissue.

In the case of solitary deposits, the parenchyma, with the exception of that adjoining the morbid product, does not participate in the local process; when they are very extensive, reaction takes place throughout the organ, and is evidenced by tumefaction, enlargement, softening, and and infiltration of the parenchyma; even the mucous membrane of the urinary passages appears congested, reddened, and softened.