CHAPTER XI 



THE ALBUMINOIDS 



THIS group comprises a series of albuminous substances, which form 

 the supporting structures of animals, or the * connective tissues ' of 

 the histologist. They do not form a part of the cell, but are structures 

 which have been secreted by the cells, the latter during the formation of 

 the supporting tissues -becoming included in the secretions. Albuminoids 

 are absent in the nutritive fluids of animals, such as the blood and the 

 lymph. (Glutolin is dealt with on p. 567.) 



The term albuminoid is thus an anatomical one, and comprises 

 chemically most divergent substances. Gelatine besides heteroalbu- 

 mose, is the only pure ' an ti- albumin,' for tyrosin and tryptophane 

 are absent, while glycocoll and bases are present in large quantities. 

 Keratin contains more cystin than does any other albumin, and there- 

 fore more sulphur ; it also contains much tyrosin ; elastin is so poor 

 in bases as to resemble some plant-albumins. Fibroin is composed of 

 more than 50 per cent of alanin and glycocoll. Amyloid ought, 

 perhaps, to be classed amongst the proteids, because of its large 

 amount of chondro- sulphuric acid. In days to come, when the 

 chemical classification of albumins is more advanced, albuminoids will 

 be brought under quite different headings, for the present arrangement 

 serves simply as a makeshift. 



Albuminoids are as much albumins as are the soluble albumins, 1 

 and it is arbitrary to still classify them as 'substances resembling 

 albumins,' for the differences between gelatine and keratin and the 

 albumins are by no means greater than are those between the 

 albumins and casein or globin. 



Chemically, albuminoids are albumins, for they are split up by 

 acids or ferment into albumoses, peptones, and amino-acids ; with 

 halogens they give rise to substitution-products ; they form salts ; they 



1 A. Kossel, Ber. d. deutsch. chem. Ges. 34. III. 3214 (1901). 

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