32 PHYSIOLOGICAL CHEMISTRY. 



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

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

 mucin also occurs in the connective tissue and navel-cord. Some- 

 times, as in snails and in the membrane of the frog-egg (GiACOSA), 

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

 which may be converted into mucin by alkalies. Mucoid substances 

 are found in cartilage, certain cysts, etc. As the mucin question 

 has been very little studied, it is at the present tiij.e 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. So much 

 is sure, that mucins or nearly-related bodies occur widely diffused in 

 the organism of certain tissues. From their decomposition prod- 

 ucts we derive a great deal of knowledge in regard to the forma- 

 tion and splitting of carbohydrates or kindred bodies (glycuronic 

 acid) from other complex atoms. 



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

 mucins in a pure and unchanged condition due to the reagents 

 used. The elementary analyses of these mucins have given the 

 following results : 



C H N S O 



Mucin from snail 5032 6.84 13.65 1.75 27.44 (HAMMARSTEN.) 



Mucin from nerve 48.30 6.44 11.75 0.81 32.70 (LOEBISCH.) 



Mucin from sub-maxillaris 48.84 6.80 12.32 0.84 31.20 (HAMMARSTEN.) 



The mucin of the snail-skin, which stands closest to keratin, 

 contains more sulphur than the other mucins. The sulphur is 

 moreover, at least in certain mucins, part in loose and part in strong 

 chemical union. 



By the action of superheated steam on mucin a carbohydrate, 

 animal gum (LANDWEHR), is split off. On boiling mucin with 

 dilute mineral acids, acid albuminate and bodies similar to albu- 

 mose or peptone are obtained, besides a reducing substance which 

 has not been closely studied. By the action of stronger acids we 

 obtain among other bodies leucin, tyrosin, and laevulinic acid 

 (LAISTDWEHR). Certain mucins, as the submaxillaris mucin, are 

 easily changed by very dilute alkalies, as lime-water, while others, 

 such as nerve-mucin, are not affected (LOEBISCH). If a strong 



