536 CHEMISTRY OF THE PROTEIDS CHAP. 



Mucin is salted out by saturated sodium-chloride and magnesium- 

 sulphate solutions ; the limits for ammonium sulphate in the case of 

 bile mucin are 3 '2 and 4*6, according to Brauer. 



Mucin is very resistant to acids, but is readily denaturalised by 

 alkalies ; if it be kept for some time in feebly alkaline solutions, it is 

 at first still precipitable by means of acetic acid like a typical mucin, 

 but soon it gives rise to a slight flocculent precipitate, and finally the 

 whole of the mucin is thrown down as flocculi, and whenever this 

 happens the solution has lost its typical slimy character, and has 

 become a limpid solution. The mucin is changed by alkalies into an 

 alkali-albuminate, and then possesses different properties and a different 

 composition, for it is now readily precipitated by salts, and may be 

 precipitated by acids if great care be taken in exactly neutralising the 

 solution, as the neutralisation-precipitate is at once dissolved by the 

 smallest excess of acid. The alkali-albuminate differs from mucin 

 further in being precipitated by potassium ferrocyanide + acetic 

 acid. If stronger solutions of alkali are allowed to act on mucin a 

 well-marked giving off of ammonia may be observed. Similar obser- 

 vations were made by Drechsel and Mitjukoff l with the closely related 

 para-mucin, and by K. A. H. Morner 2 and others with the mucoids. 

 In addition to alkali-albuminates, there occur, after some time, in 

 denaturalised mucin solutions, also albumoses possessing the usual 

 characteristics. 



Animal gum, discussed on p. 538, is formed by the action of 

 stronger alkalies. (See also the index.) 



With pepsin and trypsin, mucin dissolves to a clear, watery solution, 

 containing probably albumoses, according to Friedrich Miiller 3 and 

 Mitjukoff ; l a splitting off of a carbohydrate or other well-marked 

 radical has not been observed. 



Towards putrefaction, according to Miiller 3 and Giacosa, 4 mucins 

 are very resistant, " as their peculiar physical property makes the 

 entrance of putrefactive bacteria a difficult matter, and as bactericidal 

 bodies may also play a part " (Cohnheim). The real reason, according 

 to experiments made by the author, is the acid nature of the mucins. 



With alkalies and the alkaline earths mucin forms soluble soaps ; 

 the naturally occurring mucin is sodium mucinate, according to Miiller. 



To prepare chemically pure mucins is very difficult, as even in 

 strongly mucilaginous fluids they are present in only very minute 



1 Kath. Mitjukoff, Dissert, Bern, Arch. f. Gynak. 49. fasc. 2 (1895). 



2 K. A. H. Morner, Scandinav. Arch. f. Physiol. 6. 332 (1895). 



3 Fr. Miiller, Zeitschr. f. Biol. 42. 468 (1901). 



4 P. Giacosa, Zeitschr. /. physiol. Chem. 7. 40 (1882). 



