MUCOID DEGENERATION 431 



acetic acid, and its physical properties when in solution are quite 

 characteristic. The term mucin, however, probably covers a number 

 of related but distinct bodies. Some, such as the pseudotnucins, are 

 readily distinguished by not being precipitated by acetic acid, and 

 by being alkaline in reaction; others yield reducing substances with- 

 out previous decomposition with acids (paramucin); while even among 

 the "true" mucins certain differences in solubility exist. ^^ The studies 

 of Levene^^ indicate that the non-protein radicals of mucins are of 

 two sorts: One, chondroitin-sulphuric acid, contains the nitrogenous 

 hexose, chondrosamine, and is found in cartilage, tendons, aorta and 

 sclera; the other, mucoitin-sulphuric acid, has as its carbohydrate 

 chitosamine, and is found in gastric and umbilical cord mucin, vitreous 

 humor, cornea and ovarian cysts. 



In the mammalian body we find mucin occurring in two chief lo- 

 calities: (1) as a product of secretion of epithehal cells; (2) in the 

 interstices of connective tissue, especially of tendons. ^^ (The resem- 

 blance of synovial fluid to mucin is more physical than chemical.) 

 There is also evidence that mucin or a related body constitutes the 

 cement substance between all the body-cells. Corresponding to these 

 two chief sources of mucin we find mucoid degeneration occurring as 

 distinct processes in mucous membranes (or tissues derived therefrom) 

 and in connective tissue. 



Epithelial Mucin. — As epithehal mucin represents a distinct 

 product of specialized cells, it is questionable if the ordinary applica- 

 tion 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 mem- 

 branes (the so-called "colloid 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 proteins derived from cell degeneration or from 



'" For special consideration see Cutter and Gies, Amer. Jour. Phvsiol., 1901 

 (6), 155. 



'"■ Jour. Biol. Chem., 1918 (36), 105. 



'^ Schade (Zeit. exp. Path., 1913 (14), 23) says that the long controversy 

 concerning the intercellular substance of mammalian connective tissue is settled 

 by the work of Lier (Ledermarkt-Collegium, Frankfurt, 1909, p. 321), who found 

 it to be a mucin similar to that of tendon or umbilical cord. Its behavior in 

 edema supports this observation. That there are some chemical similarities in 

 the protein moiety of epithelial and tendon mucin is indicated by their immuno- 

 logical inter-reactions (Elliott, Jour. Infect. Dis., 1914 (15), 501). 



