As =secondary= causes are those in which the inflammation starting in the uriniferous tubes extends down to and implicates the pelvis, and the still more frequent instances of extension of purulent infection upward from the ureter, bladder or prostate, so as to involve the pelvis. So in blocking of the urethra by strongylus, stricture, clot or calculus, and in spasm of the sphincter vesicæ, the delayed urine is liable to undergo fermentation with evolution of ammonia, and not only the bladder but the ureter and renal pelvis may suffer. Again, the occurrence in the kidney of the hyperplasia of cancer, glanders (horse) and tuberculosis (cow) may be the direct cause of pyelitis. Similarly foci of infection in the kidney may be found in distemper in the dog, and in the contagious pneumonia and influenza of the horse. In man infection from the bowel through the migration of the bacillus coli communis to the devitalized kidney and contents in hydronephrosis, has been traced, and the liability to this must be still greater after the surgical insertion of the ureters in the rectum as a substitute for the obliterated bladder and urethra. Again, in the intra-arterial migrations of the strongylus (sclerostoma) armatus pus microbes may be carried to the kidney and reach the pelvis. _Symptoms._ These are in the main those of nephritis with marked rigors. The presence of pus cells and albumen in the urine may come from suppuration in the substance of the kidney itself, or sub-capsular abscess opening into the pelvis, or it may come from cystitis, prostatitis or urethritis. The special stiffness and tenderness of the loins, polyuria in which the liquid is purulent, but free from uriniferous casts, and in which it is charged with the spheroidal epithelium of the pelvis (not the columnar of the tubules), may afford presumptive evidence of pyelitis. But pyelitis is usually combined with nephritis or cystitis and the complications prevent diagnosis. In some cases the urine is scanty and strongly albuminous, and in others a round calculus will block, at intervals, the opening of the ureter giving rise to obstruction of the flow from that kidney and the occurrence of violent renal colic lasting until the stone is again dislodged backward. _Diagnosis_ cannot often be certain. Purulent urine, with a considerable number of the spheroidal cells of the pelvis, and the general signs of nephritis may be taken as diagnostic. A great excess of such epithelial cells would on the contrary point to cystitis.