A peculiar lesion occasionally seen in birds is “uratic pericarditis” a process not infectious at all, according to Plimmer, but due to renal disease. It has been seen here in association with retention of urates in the kidney, with gout of birds, and apparently quite independent of any renal or constitutional disease. Both layers of the sac are pearl gray or irregularly salted with a whitish granular material so that they are entirely opaque; occasionally the distribution is spotty. The deposit does not seem to penetrate the myocardium. There is at times some involvement of other serosæ, but this is usually much less marked than around the heart. It does not seem that this of itself should be fatal, but it has been the most decided pathological factor in some of the autopsies. Aside from pericarditic exudates, twenty-one instances of pericardial effusion have been encountered. They offer little that is peculiar in etiology, chemistry or cytology, but as there has been some question of the position of the accumulation of the fluid in human beings, it might be well to note the position in our material. It is recognized in veterinary medicine that the cardiac dullness is increased especially to the right, and that most of the fluid will be on that side and posteriorly. At our autopsies on mammals this is the position usually occupied by the fluid, the apex being covered by pericardium, unless the quantity be great enough to make the sac taut, and this position is retained whether the animal be laid upon the one side or the other; nor does the fluid all leave the base of the heart when the body is placed prone. The crown of the heart is nearly always well covered. In birds, on the other hand, the fluid occupies the apical part of the sac, probably due to the fact that this membrane is attached by its tip to the transverse air sac wall which takes the place of a diaphragm, so that the tip of the heart is always free and the pericardium of the base fairly closely applied to the epicardium. This holds good even for the birds whose cardiac apex is normally attached to the pericardium by a fibrous band. HYPERTROPHY AND DILATATION.