MUCOID DEGENERATION 357 



Epithelial Mucin. As epithelial mucin represents a dis- 

 tinct product of specialized cells, it is questionable if the ordi- 

 nary application of the term degeneration, in the sense of the 

 conversion of cell-protoplasm into mucin, is correct. Certainly 

 the mucin formation of catarrhal inflammation is merely an 

 excess of a normal secretion, and the degenerative changes that 

 may be present in the epithelial cells are produced by the cause of 

 the inflammation, and are not dependent upon mucin formation. 

 Even in the extreme example of mucoid degeneration seen in 

 carcinomas derived from mucous membranes (the so-called "col- 

 loid cancers "), the epithelial degeneration is not necessarily to 

 be interpreted as a conversion of cell-cytoplasm into mucin, 

 but is largely due to the pressure of secreted mucin upon the 

 cells within the confined spaces of the tumor. The mucin in 

 these forms of mucoid degeneration is chemically the same as 

 the normal mucin coming from the same source, but mixed with 

 larger or smaller quantities of other proteids derived from cell 

 degeneration or from vascular exudates. (The stringy, mucin- 

 like substance seen in some purulent exudates is probably com- 

 posed largely of nucleoproteids and nucleo-albumins derived 

 from the degenerating leucocytes, and is not true mucin.) 



Connective-tissue Mucin. Excessive formation of con- 

 nective-tissue mucin is observed most characteristically in myx- 

 edema ( q. v. ), but may also occur in connective tissues that are 

 poorly nourished or otherwise slightly injured ; it is seen partic- 

 ularly in the connective tissues surrounding the epithelial ele- 

 ments in adenomas and carcinomas. Connective-tissue tumors 

 (myxosarcoma, myxofibroma, or myxoma) may also show a 

 great quantity of mucinous intercellular substance, but many 

 of the so-called myxomas are in reality merely edematous 

 fibromas or polypoid tumors, in which the resemblance to true 

 myxoma is largely structural rather than chemical. This form 

 of mucoid degeneration seems to be merely a reversion to the 

 fetal type of connective tissue, which is characterized, as in the 

 umbilical cord, by an excessive accumulation of a mucin-con- 

 taining fluid intercellular substance, and a paucity of collagen- 

 ous fibrillar structure. Apparently, when connective tissue 

 reverts to an embryonal type, either from intrinsic causes (tumor 

 formation), or when the nourishment is insufficient, or possibly 

 when the normal stimulus to cell growth is absent (myxedema), 

 the mucoid characteristics of fetal tissue reappear. 



The presence of mucin in the tissues seems to cause no 

 reaction, and its absorption causes no harm. Rabbits that I 

 injected with large quantities of pure tendon mucin almost daily 



