The appearances of the substance of the tumor are not uniform. In many cases the color of the interior of the tumor is dark gray; in some it is dull red; again, sometimes almost livid. The surface of the tumor after the capsule has been removed is often marked by sulci denoting a division into lobules. In other cases the tumor is smooth and symmetrical in shape, and the fibres distinctly visible to the naked eye. The smooth tumor is apt to be very dense and comparatively difficult to destroy, while the lobulated variety is less dense and sometimes easily broken to pieces. But the difference of density does not correspond altogether with the color or shape of surface. We seldom find large tumors of uniform structure. In some places they are of solid fibrous structure; in others there are cavities of greater or less size, containing a tenacious red serum. These cavities, which seem to be made by localized disintegration of the fibrous tissue, are sometimes of great size, containing several pounds of serum (Atlee). Much more frequently they are small and hold a small amount of fluid. I have met with several where the substance of the tumor seemed to be made up of alveoli filled with a tenacious fluid the color of milk. Besides this effect upon the density of the tumor resulting from what might be called its usual course, there are numerous modifications in it and in the other properties of the tumors arising from spontaneous degeneration. It may be said, I think, that without adventitious or supplementary vascular supply the life of a fibrous tumor is self-limited, and it ceases to grow after it has attained to a certain size, and that then it either remains stationary or undergoes degeneration. As I shall have occasion to say farther on, the original supply of blood-vessels cannot be increased to an indefinite degree, and the tumor that grows indefinitely derives a supplementary supply of blood by contracting adhesions to the viscera or abdominal walls. Such adhesions are common and mischievous. After a tumor has attained its growth, degeneration into the more elementary forms of tissue sets in, as the cartilaginous degeneration, and there is often a deposition of earthy material found in it which reduces it to a hard, dense, stationary, and indestructible body. In such cases there is almost a complete loss of vitality in the tumor, and it becomes a calcified mass. We may easily demonstrate that the structure of these tumors is essentially fibrous. By maceration and careful dissection the fibres are traceable to a greater or less degree in all of them, the proportion and characters of which, as before said, differ greatly. In the smooth, symmetrically-developed tumor the fibres are usually long and distinctly traceable, while in the lobulated light-gray tumor the fibres are more rudimentary and not so easily followed up by dissection.