The disease may, however, begin with the auricles, owing to disease of the auriculo-ventricular valves impeding the flow of blood into the ventricle, or to simple narrowing of the auriculo-ventricular opening. The auricle is then primarily enlarged, the corresponding veins congested, this is propagated to the capillaries and arteries, and lastly the ventricle on the opposite side of the heart is involved. This is chiefly seen with fibrinous deposits on the valves or in the case of polypus hanging into the auriculo-ventricular opening. Aneurisms, embolisms, neoplasms, atheroma and calcic degeneration of the arterial walls may be effective factors. In addition to these causes Bouilaud and Leblanc attach a high importance to chronic inflammations of the serous membranes, which by reason of the contiguity of the latter to the muscular structure bring about a more abundant circulation in this and an increased nutrition. Another cause is unintermitting hard work which necessitates excessive exertion of the heart, to supply blood more freely to the muscular system and the lungs. Many hunters suffer from this affection it is believed because of their extraordinary exertions. The stallion Helenus had a heart of 14 ℔s. _Weight of the heart._ The heart in the horse which rarely weighs over 9 ℔s. is increased from 10 ℔s. to 14 ℔s. in this disease and in one case in a cart horse, recorded by Stephenson in the Veterinarian for 1861, it is said to have reached 32 ℔s. Stephenson probably weighed the heart while filled with blood. A diseased heart weighed in this way by Thomson amounted to 34 ℔s., one by Gerlach, 19 ℔s., an ox’s heart by Herran 36 ℔s. In Stephenson’s case there was further an extraordinary dilatation of the anterior vena cara. Haycock (Veterinarian, 1850), records a case in which though the heart only weighed 10 ℔s. 8 oz., yet the walls of the ventricles were double the normal thickness, those of the left being 2¼ inches while those of the right were 1 inch. An estimate from the thickness of the walls, it must be borne in mind, is not so satisfactory as the absolute weight taken after the removal of the large vessels, the superfluous fat and the contained blood.