COLLOID DEGENERATION 355 



writers, the mucoid degeneration of carcinoma. Ziegler rightly 

 protests against the inclusion of mucin under this heading, but 

 includes the corpora araylacea. On account of the discovery 

 by Baumann of the specific chemical nature of thyroid colloid 

 it becomes particularly unfortunate that the term " colloid " has 

 such a wide and uncertain application. It would seem that the 

 safest view to take is that the word colloid is merely morphologic- 

 ally and macroscopically descriptive of certain products of cell 

 activity or disintegration, which have nothing in common 

 except the fact that they form a thick, glue-like or gelatinous, 

 often yellowish or brownish substance. There is no one definite 

 substance colloid, according to the usual usage of the word in 

 pathological literature, but many different proteid substances 

 may assume the appearance to which the name " colloid " is 

 given. Looking at the matter in this way, we must recognize 

 as the usual "colloid" substances, the following chemical 

 bodies : 



Thyroid colloid, the physiological prototype of the group. 

 This consists of a compound of globulin with an iodin-contain- 

 ing substance, thyroiodin, the compound proteid being called by 

 Oswald iodothyreoglobulin. It occurs pathologically only in 

 cystic and similar changes in the thyroid or accessory thyroids. 

 Being a specific product of the thyroid (and perhaps of the 

 hypophysis) with definite physiological properties, it manifestly 

 has only a morphological relation to the other forms of colloid 

 found in degenerating tumors, etc. (The nature of thyroid 

 colloid is discussed more fully under " Diseases of the Thy- 

 roid," Chap, xx.) 



Mucin, when secreted in closed cavities, as in tumors, where 

 it becomes thickened by partial absorption of the water, may 

 take on a " colloid " appearance while retaining its chemical and 

 tinctorial characteristics. This is particularly observed in the 

 " colloid " carcinomas which arise especially from the mucous 

 membrane of the alimentary tract. This substance is, of 

 course, quite specific both in its chemical nature and its origin 

 from specialized epithelial cells, and the process should properly 

 be considered as a " mucoid degeneration." 



Psetldomucin, which differs from mucin in not being pre- 

 cipitated by acetic acid, is a common component of ovarian 

 cysts, and when somewhat concentrated by absorption of water, 

 forms a " typical colloid." Because it is alkaline, this form of 

 colloid tends to stain rather with the acid dyes (eosin, fuchsin, 

 etc.), while true mucin stains with basic dyes. Several varieties 

 of pseudomucin have been described by Pfannenstiel, and their 



