44 THE ALBUMINS. 



and are of special importance as food-stuffs. Some of them also 

 contain iron. They possess markedly acid properties, and can 

 hence combine with bases to form salt-like products. Most of the 

 nucleo-albumins are insoluble in distilled water, in neutral salt 

 solutions, and in weak acids, while they dissolve with ease in the 

 presence of a small amount of an alkaline hydrate or lime-water. 



The most important member of this group, casein, occurs in solu- 

 tion in the milk as a calcium compound. In combination with the 

 alkalies or the alkaline earths, the nucleo-albumins dissolve in water 

 upon the application of heat, and it is to be noted that such solu- 

 tions do not coagulate on boiling. Coagulation occurs, however, as 

 in the case of the albumins proper, as soon as the basic component 

 is removed by means of an acid. 



Other nucleo-albumins, such as those which can be obtained from 

 the yolk of birds 7 eggs, and leucocytes, are soluble in dilute acids and 

 in a 10 per cent, saline solution, but are also insoluble in water. 

 From their solutions they are partly coagulated by heat. Pepsin 

 in the presence of 0.2 per cent, of hydrochloric acid decomposes 

 the nucleo-albumins with the liberation of the nuclei ns. 



The Glucoproteids. In the glucoproteids an albuminous radicle 

 is combined with a carbohydrate group, or a carbohydrate deriva- 

 tive which may or may not be nitrogenous. They all contain carbon, 

 hydrogen, nitrogen, oxygen, and sulphur. In addition, phosphorus 

 has been found in certain representatives of this group, and these 

 have accordingly been termed phosphoglucoproteids. The gluco- 

 proteids proper comprise the mucins, the mucoids or mucinoids, 

 and the hyalogens, all of which are peculiar to the animal world. 

 Of the phosphoglucoproteids, on the other hand, only two repre- 

 sentatives are known at the present time, viz., the ichthulin of carp 

 eggs, and the helicoproteid which may be obtained from the albu- 

 minous gland of Helix pomata. 



The carbohydrate radicle, which may be separated from the albu- 

 minous group on boiling with dilute mineral acids, is apparently not 

 the same in all glucoproteids, and in most cases its true chemical 

 nature has not as yet been ascertained. From certain mucins, 

 Landwehr claims to have obtained the so-called animal gum, 

 which is a dextrin-like carbohydrate, when the substance was ex- 

 posed to the action of superheated steam. On carrying the decom- 

 position further, as on boiling with strong mineral acids, Irevulinic 

 acid was found, besides leucin, tyrosin, and other bodies of this 

 order. 



From the helicoproteid Hammarsten succeeded in splitting off a 

 gum-like dextrorotatory substance, which he regards as animal 

 sinistrin. 



Beyond these few data, however, practically nothing is known of 

 the character of the reducing substance. 



While all glucoproteids show a structural composition which 

 warrants their classification as a separate group of proteids, the 



