x THE GLYCO-PROTEIDS 531 



The properties of this carbohydrate have already been discussed 

 from p. 154 to p. 164. It is an unknown animated polysaccharid which 

 does not reduce, and the amino-group of which is not free ; on being 

 boiled with alkalies or with acids it gives rise to glucosamin. In the 

 case of the mucin forming the covering of the eggs in frog's spawn 

 glucosamin is replaced by galactosamin, according to Schulz and 

 Ditthorn ; l while in chondro-mucoid its place is taken by a hexo-amino 

 acid, according to Orgler and Neuberg. 2 Neuberg 3 has found in the 

 albumin prepared from the yolk of the egg, in addition to glucosamin, 

 another carbohydrate acid. 



Glyco-proteids differ from the nucleo-proteids and from haemo- 

 globin in not readily dissociating into the albumin moiety and the 

 prosthetic group. The carbohydrate is only set free by boiling with 

 mineral acids or by the intense action of alkalies, and by both of these 

 procedures the albumin fraction is broken up into crystalline dissocia- 

 tion-products or at least into albumoses. For this reason, and also 

 because other albumins contain a carbohydrate-radical (p. 356), it is 

 doubtful whether we are justified in making a special group of " glyco- 

 proteids." It is quite possible that in the so-called glyco-proteids we 

 are only dealing with a group of albumins in which one of the dis- 

 sociation-products, namely, the sugar-radical, is present in a larger 

 amount than in the ordinary albumins. 



To the glyco-proteids belong the mucins and related compounds, 

 the egg-albumin and the little understood phospho-glyco-proteid. Egg- 

 albumin has already been dealt with amongst the albumins on p. 353, 

 and, therefore, only the sharply defined and readily recognisable class 

 of mucins and mucoids will be discussed now. 



Eichwald 4 was the first to observe that a reducing substance may 

 be separated from mucin, and he was the first to regard mucins as 

 composed of an albumin -f a sugar-radical. The nature of the mucins 

 was subsequently most thoroughly investigated by Hammarsten, and he 

 defined accurately the features of this group of proteids. The sugar- 

 radical has been most thoroughly investigated by Muller, as already 

 explained on pp. 154-164. 



The mucins and mucoids are acid compounds, containing no 

 phosphorus, and yielding a reducing substance on being boiled with 

 acids. Their percentage-composition is remarkable for the low carbon- 



1 F. N. Schulz and F. Ditthorn, Zeitschr. f. physiol. Chem. 29. 373 (1900) ; 32. 

 428 (1901). 



2 A. Orgler and C. Neuberg, ibid. 37. 407 (1903). 



3 C. Neuberg, Ber. d. deutsch, chem. Ges. 34. III. 3963 (1901). 



4 A. Eichwald, Liebig's Annalen 134. 177 (1865). 



