78 MUCIN. 



The mucin of Helix pomatia 1 . Hammarsten distinguishes between 

 the mucin contained in the secretion of the mantle and that which may 

 be derived from the foot of this animal. Mantle-mucin. The secretion 

 of the mantle contains a mucigenous substance precipitable by acetic 

 acid which is exceedingly insoluble in water, but is readily converted 

 into true mucin by the action of dilute ('01 p.c.) caustic potash. From 

 its solution in alkali it may be purified by precipitation with acetic acid, 

 washing, re-solution in alkali and reprecipitation with acid. When dis- 

 solved in a trace of alkali the solution yields the reactions typical of 

 other mucins, but it differs from these in the fact that the precipitate 

 formed on the addition of hydrochloric acid (or acetic) is not soluble in 

 excess of the acid. Foot-mucin. It may be obtained by extracting the 

 foot with '01 p.c. KHo ; from this solution it is now precipitated by the 

 addition of hydrochloric acid (not acetic) up to ! '2 p.c., redissolved in 

 alkali and reprecipitated with acid, the process being repeated several 

 times. Solutions of this mucin resemble those of mantle -mucin in all 

 essential respects, the only difference which is stated to be characteris- 

 tic of the two being that in presence of sodium chloride, mantle-mucin, 

 like that of the submaxillary gland, is not precipitated by faint acidu- 

 lation with acetic acid, whereas under similar conditions solutions of 

 foot-mucin cannot even be neutralised without yielding an opalescence 

 or precipitate. 



The mucin of tendons' 2 . The tendo Achillis of the ox is cut into 

 thin slices, washed with distilled water and extracted with half-saturated 

 lime-water ; the mucin is thus dissolved and is purified by precipitation 

 with either acetic or hydrochloric acids, re-solution in dilute alkali and 

 reprecipitation with acids. In its general reactions it resembles the 

 mucins, previously described, but appears to differ from them in its 

 distinctly greater resistance to the action of acids and alkalis. 



Mucin of the umbilical cord 3 . May be extracted by means of water 

 and is readily precipitated from the solution by acetic acid. It appears 

 to differ from the other mucins in containing more nitrogen and a con- 

 siderable amount of sulphur : it lies in fact somewhat midway between 

 the proteids and true mucins. 



By prolonged boiling with sulphuric acid mucins yield leucin and 

 tyrosin, but the products of their decomposition have not been as yet 

 fully studied 4 . 



Analyses of the several mucins exhibit differences in percentage 



1 Hammarsten, Pfliiger's Arch. Bd. xxxvi. (1885), S. 373. Gives previous 

 literature. 



2 Lobisch, Zt. f. physiol. Chem. Bd. x. (1886), S. 40. Gives previous literature. 



3 Jernstrom (Swedish). See Abst. in Maly's Bericht. 1880, S. 34. 



4 Walchli, Jn.f.prakt. Chem. N.F. Bd. xvn. (1878), S. 71. 



