Under this name are included conditions in which the cells of structures secrete or become converted into a clear homogeneous substance, this transformation implying the destruction of the cells. It occurs almost as a physiological process in the Thyroid gland, as colloid matter is always present in later life in that gland. It forms an important element in the commonest form of Goitre, in which there is an enlargement of the gland. The thyroid gland consists of saccules lined with epithelium. The epithelial cells become colloid and the saccule comes to be occupied by a translucent clump of colloid matter, which by swelling up causes enlargement of the saccule. In the Kidneys we frequently find cysts occupied by colloid matter, which has arisen by transformation of the epithelium of the tubules or Malpighian bodies.