78 MUCIN. 



and hydrochloric acid is added up to 1 15 p.c. The mucin is 

 thus precipitated at first, but at once passes into solution, from 

 which it is precipitated by the addition of a volume of water equal 

 to three to live times that of the original solution. This precipi- 

 tate is then again dissolved in dilute hydrochloric acid and repre- 

 cipitated by water, the process being repeated several times. As 

 thus prepared and thoroughly washed it possesses a distinctly 

 acid reaction ; it may be dissolved to a neutral solution by the 

 cautious addition of very dilute alkalis, and now exhibits the fol- 

 lowing properties. It is readily precipitated by acetic acid, much 

 less readily in presence of sodium chloride ; this salt on the other 

 hand greatly facilitates the precipitation of mucin by alcohol, which 

 again does not take place in presence of a trace of free alkali. 

 Any excess of alkali, especially on warming, at once changes the 

 substance so that its characteristic ropiness is permanently lost, 

 and boiling with dilute mineral acids yields a reducing substance. 

 It gives the usual reactions for proteids and is strongly precipi- 

 tated by the acetates of lead and by CuS0 4 and by excess of NaCl 

 and MgS0 4 . 



The mucin of Helix pomatia. 1 Hammarsten distinguishes be- 

 tween 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 sub- 

 stance 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 dissolved 

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

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

 tate 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 characteristic of the two being that 

 in presence of sodium chloride, mantle-mucin, like that of the 

 submaxillary gland, is not precipitated by faint acidulation 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? The tendo Achillis of the ox is cut into 



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. 



