CLASSIFICATION 429 



bases, such as guanine, adenine, xanthine, etc. (see p. 376). 

 The view of Jones * on the nature of nucleo-protein is 

 that the term connotes a salt of protein with nucleic acid 

 in which the protein is in excess ; when submitted to 

 peptic digestion, part of the protein is removed, leaving 

 a salt containing rather less of the base and consequently 

 of a more acid nature to which the name nuclein was 

 at one time given. He concludes that the term nucleo- 

 protein " means rather a method of preparation than a 

 chemical substance." 

 Derivatives of Proteins. — In this group are included a number 

 of substances obtained by the hydrolysis of proteins ; 

 they may be sub-divided as follows : — 



1. Meta-proteins, consisting of acid albumin and 

 alkali albumin, produced respectively by the action of 

 acid or alkali on proteins. 



2. Proteoses, represented by albumose, globulose, 

 gelatose, etc. These substances are produced from pro- 

 teins by the action of digestive juices such as pepsin and 

 trypsin. 



Pepsin, which acts in an acid medium, breaks up the 

 protein as follows : — 



Protein. 



Meta-protein (acid albumin). 



Primary Proteose (precipitated by half-saturated ammonium 

 sulphate and by potassium ferrocyanide in the presence of 

 acetic acid). 



Secondary Proteose (precipitated by saturated ammonium sul- 

 phate, but only slowly by potassium ferrocyanide in the 

 presence of acetic acid). 



Peptone (not precipitated by saturated ammonium sulphate nor 

 by potassium ferrocyanide in the presence of acetic acid). 



Polypeptides and Amino Acids. 



The formation of amino acids from peptones takes 

 place only after prolonged action. 



Trypsin, which acts in an alkaline medium, produces 

 substantially the same series of changes, only that the 

 meta-protein in this case is alkali albumen ; furthermore 

 the decomposition into amino acids takes place more 

 rapidly than with pepsin. 



* Jones : " Nucleic Acids," London, 1920, p. 7. 



