THE GLYCO-PROTEIDS : MUCIlT ' 537 



quantities. Mucin-solutions do not filter at all readily, and the 

 tough mucin-coagula settle only very slowly. Finally, there is always 

 the danger of denaturalisation by means of alkalies or by alcohol. 



2. Bile Mucin 



From the bile of man and dogs mucin may be directly precipitated 

 by the addition of acetic acid or of alcohol, as no other albuminous sub- 

 stances are present, but a disadvantage is that this mucin is contami- 

 nated by bile salts and bile pigments, which Paijkull 1 had great diffi- 

 culty in removing by long -continued dialysis. The mucin of the 

 submaxillary gland Hammarsten prepares as follows : The gland is ex- 

 tracted with water, and then hydrochloric acid is added to the extract 

 to the extent of O'l to 0'2 per cent. By this means mucin and the 

 abundantly present nucleo-proteid are both thrown down, but they soon 

 pass into solution again. On diluting this solution containing hydro- 

 chloric acid with four times its volume of distilled water, the mucin is 

 again precipitated, while the nucleo-proteid is still kept in solution by 

 the dilute hydrochloric acid. The mucin so obtained is then carefully 

 dissolved in very dilute caustic-potash solution, or even better in 

 ammonia, every precaution being taken to prevent the reaction from 

 becoming alkaline. The dissolved mucin is then precipitated with 

 acetic acid ; again dissolved in an alkali, reprecipitated with acetic 

 acid, and this procedure repeated once more. The mucin from the 

 snail was prepared similarly. 



3. Bronchial Mucin 



The mucin of the respiratory passages Friedrich Miiller 2 prepared 

 from the glassy, purely mucous sputum of patients suffering from 

 chronic bronchitis. The mucin is freed as much as possible from 

 admixtures of pus, food particles, etc., and is then precipitated with 

 alcohol ; the albumin and nuclein are thrown down as flocculent 

 precipitates, while the mucin separates out as fine fibres, which may 

 be separated mechanically from the albumin, etc. The mucin is now 

 repeatedly washed with very dilute hydrochloric acid (G'l-0'2 per cent) 

 and soda-solution, dissolved in very dilute caustic soda, precipitated 

 with acetic acid, and the fibrous precipitate purified by dialysis. The 

 mucin obtained in this way is free from albumin and nucleo-proteid s, 

 and with dilute soda-solution still gives an opalescent mucilaginous 



solution. 



1 S. Paijkull, Zeitschr. /. physiol. Chem. 12. 196 (1887). 

 2 Fr. Miiller, Zeitschr. f. Biol. 42. 468 (1901). 



