MUCINS. 169 



solutions, or solutions prepared by the aid of a trace of alkali, are mucilagi- 

 nous,' ropy, and give a precipitate with acetic acid which is insoluble in 

 excess of acid or soluble only with great difficulty. The mucoids do not 

 show these physical properties, and have other solubilities and precipit- 

 ation properties. As we have intermediate steps between different pro- 

 tein bodies, so also we have such between true mucins and mucoids, and 

 a sharp line cannot be drawn between these two groups. 



It is just as difficult at present to draw a sharp line between the pro- 

 teins and the mucins or mucoids, since we have been able to split off 

 carbohydrate complexes from several proteins, and as proteins have 

 been isolated from white of egg which yield more or less glucosamine. 

 The very variable amounts of glucosamine obtained under various con- 

 ditions from the crystalline ovalbumin seem to indicate that we are 

 dealing with a contamination with a glycoprotein. 



True mucins are secreted by the larger mucous glands, by certain 

 mucous membranes, and by the skin of snails and other animals. True 

 mucin also occurs in the navel-cord. Sometimes, as in snails and in 

 the membrane of the frog-egg (GIACOSA) and perch-eggs (HAMMARSTEN 1 ), 

 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 LEVENE and of CUTTER, and GiES, 2 contains 

 chondroi tin-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 

 sufficiently 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 (Fn. MULLER 3 ) 



Mucin from submaxillary 48 . 84 6 . 80 12 . 32 . 84 (HAMMARSTEN 3 ) 



Mucin from snail 50.32 6.84 13.65 1 .75 (HAMMARSTEN 3 ) 



Synovial mucin 51 . 05 6 . 53 13.01 1 . 34 (v. HOLST 4 ) 



1 Giacosa, Zeitschr. f. physiol. Chem., 7; Hammarsten, Pfliiger's Archiv., 36, and 

 Skand, Arch. f. Physiol., 17. 



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



3 Fr. Miiller, Zeitschr. f. Biologic, 42; Hammarsten, Zeitschr. f. physiol. Chem.. 12, 

 and Pfliiger's Arch., 36. 



4 Zeitschr. f. physiol. Chem., 43. 



