MUCINS. 165 



a mother-substance of mucin, a mucinogen, has been found which may 

 be converted into mucin by alkalies. Mucoid substances are found in 

 certain cysts, in the cornea, the crystalline lens, white of egg, and in 

 certain ascitic fluids. The so-called tendon-mucin, which, according 

 to the investigations of LEVEXE and of CUTTER, and GiEs, 1 contains 

 chondroitin-sulphuric acid or a related substance, cannot be classified 

 as a mucin, but must, like the chondromucoid and the osseomucoid, be 

 classified as chondroprotein. As the mucin question has not been suffi- 

 ciently studied, it is at the present time impossible to give any positive 

 statements in regard to the occurrence of mucins and mucoids, especially 

 as without doubt in many cases non-mucinous substances have been 

 described as mucins. 



True Mucins. Thus far we have been able to obtain only a few 

 mucins in a pure and unchanged condition, because of the reagents used. 

 'The elementary analyses of these mucins have given the following results : 



c H N s 

 Mucin from mucous membrane (air- 

 passages) 48.26 6.91 10.70 1.40 (FR. MULLER 2 ) 



Mucin from submaxillary 48.84 6.80 12.32 0.84 (HAMMARSTEN 2 ) 



Mucin from snail 50.32 6.84 13.65 1 .75 (HAMMARSTEN 2 ) 



Synovial mucin 51.05 6.53 13.01 1.34 (v. HOLST 3 ) 



MULLER obtained 35 per cent glucosamine from mucous-membrane 

 mucin and 23.5 per cent from the submaxillary mucin. 



By the action of superheated steam on mucin a carbohydrate, animal gum 

 (LANDWEHR), is split off. This has not been substantiated by other investigators, 

 such as HAMMARSTEN, FOLIN and FR. MULLER. 4 Instead of a non-nitrogenous 

 gum a nitrogenous carbohydrate derivative was always obtained. 



On boiling mucin with dilute mineral acids, acid albuminate and 

 bodies similar to proteoses are obtained, besides a reducing substance 

 which is not free glucosamine (STEUDEL 5 ). By the action of strong 

 acids upon mucins or mucoids OTORI 6 obtained several of the cleavage 

 products of the proteins, such as leucine, tyrosine, glycocoll, glutamic 

 acid, oxalic acid, guanidine, arginine, lysine, and humus substances, and 

 also carbohydrate cleavage products, such as levulinic acid. Certain 

 mucins, as the submaxillary mucin, are easily changed by very dilute 



1 Levene, Zeitschr. f . physiol. Chem., 31 ; Cutter and Gies, Amer. Jourri. of Physiol., 6. 



2 Fr. Miiller, Zeitschr. Biologie, 42; Hammarsten, Zeitschr. f. physiol. Chem., 12, 

 and Pfliiger's Arch., 36. 



3 Zeitschr. f. physiol. Chem., 43. 



4 Landwehr, Zeitschr. f. physiol. Chem., 8, 9; also Pfliiger's Arch., 39 and 40; 

 Folin, Zeitschr. f. physiol. Chem., 23; Fr. Miiller, Sitzungsber. d. Gesellsch. zur Beford. 

 d. gesammt. Nat-urwiss. zu Marburg, 1896. 



5 Zeitschr. f . physiol. Chem., 34. 



6 Ibid., 42 and 43. 



