538 CHEMISTRY OF THE PROTEIDS CHAP. 



4. Snail Mucin 



The mucin of the vineyard snail, Helix pomatia, differs in many 

 respects from that of vertebrates ; it is relatively readily accessible, 

 and has there-fore been investigated repeatedly. The most minute 

 examination has been made by Hammarsten. 1 The mucin is not 

 secreted as such, but as a mucinogen which does not dissolve readily 

 even in alkalies ; when dissolved it forms a tough, not very mucous 

 fluid, which gives the reactions of mucin, but which is not precipitated 

 by corrosive sublimate. By the action of alkalies, or much more 

 slowly by mere standing in watery solutions, this mucinogen is con- 

 verted into typical mucin. The phenomenon that mucous glands 

 excrete mucinogen, which then becomes converted into mucin, has also 

 been observed by v. Uexkull 2 in the case of the sea-urchin, where the 

 change is brought about by the action of sea-water, and analogous 

 instances seem to be common amongst the invertebrates. The mucin 

 of the salivary glands of vertebrates does not pass through the mucin- 

 ogen stage, according to Holmgren, 3 but is from the very first a true 

 mucin. Considering, however, how readily the granules in mucous 

 cells are altered under the slightest provocation, the existence of a 

 mucinogen stage cannot, according to the author's opinion, be denied 

 for vertebrates. 



The mucin of the eggs of the perch, according to Hammarsten, 4 is 

 in ripe eggs normally present as a mucinogen with traces of mucin. 

 In unripe eggs there is comparatively much mucin, and hence during 

 the ripening of eggs mucin is converted into mucinogen. It yields 

 pseudo-mucin and para-mucin. 



5. Pseudo-Mucin 



Scherer 5 described in 1852 two substances from the contents 

 of an ovarial cyst which he called " metalbumin " and " paralbumin." 

 He arid subsequently Eichwald 5 could split off a sugar-radical 

 from both these substances, and Landwehr 6 prepared from them, 

 as he did out of mucin, animal gum. These substances have been 

 investigated more thoroughly by Hammarsten, 7 who first called 



1 0. Hammarsten, Pfiugers Arch. 36. 373 (1885). 



2 J. v. Uexkull, Zeitschr. f. Biol. 37- 334 (p. 388) (1899). 



3 E. Holmgren, Hammarsten's account of the Swedish papers in Maly's Jahresbericht 

 fiir Tierchemie, 27. 36 (1897). 



4 0. Hammarsten, Skand. Arch. f. Physiol. 17- 13 (1905). 



5 According to Hammarsten. 



6 H. A. Landwehr, Zeitschr. f. physiol. Chem. 8. 114 (1883). 



7 0. Hammarsten, ibid. Q. 194 (1882). 



