If in man a large venous trunk is compressed or obliterated, so that the blood no longer circulates through it, while the collateral vessels can relieve but imperfectly, dropsical effusion is sure to take place. The effusion is proportionate to the size and importance of the vein obliterated. If, for instance, in the vena cava, or large vein in the abdomen, an obstacle should prevent the return of the blood, the two lower extremities and the scrotum will become filled with serum. If the trunk of the portal vein is more or less obliterated, the serous collection takes place in the abdomen. If the obstruction occurs at the very centre of circulation, namely the heart, and the return of blood everywhere embarrassed, the dropsy becomes general, hence dropsy is one of the most common symptoms of heart disease. Dropsy is often caused by cold, applied in such a manner as to check the secretions of the skin; is often connected with eruptive diseases, as scarlatina; it may result from granular degeneration of the kidneys, debility, exhaustion from loss of blood, etc.: or from obstruction to the return of venous blood, owing to tumors, hypertrophy of the liver, glandular enlargements, etc.