There are many pathological conditions in which translucent, glancing substances appear in the tissues, and it is frequently difficult or impossible to determine the chemical and other relations of these substances, which were all at one time called colloid substances. In regard to one of them, namely, amyloid substance, the reactions are so definite that it can readily be detected even in small quantities. It has, therefore, been separated from this group. Mucin is also a tolerably definite substance, whose reactions generally allow of its detection. But even in regard to it there are cases in which its presence is doubtful, and there remain many conditions in which the colloid or hyaline appearance is visible, but the nature of the change is obscure.

Most authors use the term colloid degeneration to cover the more indefinite forms, using a term which formerly had a wider significance. Recklinghausen has introduced the term Hyalin to indicate a substance having a clear translucent appearance. This author includes under this name both solid and semi-fluid substances having the optical characters mentioned. As the term means glassy, it seems hardly consistent to call by this name tenacious fluids, such as that found in the thyroid gland in some cases of goitre. Perhaps it may be convenient to retain the term colloid for the semi-fluid matters, and hyaline for the more solid.