Pathological infiltrations of the renal structures are exceedingly uncommon. Early in our experience we were often perplexed at the appearance of certain organs, notably in carnivores and marsupials to which we were inclined to apply the term fat infiltration. However the absence of reasons for considering this picture pathological seemed sufficient cause to ignore the finding, and later Pfeiffer[39] called attention to the apparent inability of these kidneys to emulsify fat or at least to combine it in an invisible form, an ability possessed by the herbivorous organ. A monkey and a passerine bird only showed sufficient fat visible in the renal epithelium to warrant a denomination of fatty infiltration; these were both obese specimens. Amyloid infiltration occurred in four mammals and six birds, being a sequel of its usual causes, tuberculosis, chronic suppuration and osseous system disease. It is perhaps well to emphasize the fact that every organ the seat of amyloid deposit need not be enlarged. This teaching is common but I have seen human cases without enlargement and only two of the ten cases in these animals are noted as bulkier than normal. DEGENERATIONS. Degenerations represent the reaction of the kidney to toxic or infectious agents and might be considered as indicating the vulnerability of the organ. Their incidence does not coincide with that of nephritis as we shall see later. Any discussion of degenerative phenomena, and especially in the kidney, should be limited by a definition of what they are believed to be and their separation from inflammations. Degenerations are swellings, granularities, vacuolizations or infiltrations of tubular epithelium, changes which destroy the outline and internal structure, perhaps including the nucleus. No changes of the glomerular tuft or interstitial tissue are necessary for this conception since when these occur the picture becomes that of nephritis. In border-line cases it is safer to include the case under the latter heading since then the physiology is apt to be disturbed, albumen and casts appearing in the urine. Degenerations appear in various pathological states—toxemia, infection, prolonged congestion and others. The first named cause seems to be the most important in our records and the seat of the toxine production seems to be the intestine. Enteritis stands very high in the list of accompanying factors, especially in Carnivora, Primates and in Aves. Perhaps the most instructive cases are to be found in the Ungulata with toxic duodenitis. The kidney in these animals is deep red or purple, with a spanned capsule. The section surface bulges slightly, is of an opaque, dull purple color and shows a congested zone between cortex and medulla. Tubular epithelium may be found, under the microscope, sufficiently swollen to fill the lumina, in places being like ground glass, in others distinctly vacuolated. It cannot be stated absolutely which part of the