CHEMICAL COMPOSITION OF LIVING MATTER 3 



.Among the derivatives of proteins, the most important are those 

 already mentioned as being produced in protein-hydrolysis, viz. : 



(a) Meta -proteins. 



(6) Proteoses, including albumose, the proteose derived from albu- 

 min; globulose, that derived from globulin; gelatose, that derived from 

 gelatin, etc. The proteoses may be further subdivided, according to 

 the order in which they are formed in digestion into proto-proteoses, 

 hetero-proteoses, and deutero-proteoses. 



(c) Peptones. 



(d) Polypeptides. The majority of these are artificial products, 

 formed by the synthesis of amino-acids, although some can be obtained 

 from proteins by hydrolysis. Only a few of those hitherto prepared 

 give the biuret test. 



However formidable the above list may appear to the student, it 

 gives an inadequate idea of the extreme complexity of the protein class 

 and its richness in individuals. For, apart from the fact that the list 

 has been purposely left incomplete, especially as regards the numerous 

 vegetable proteins, there is the best evidence that proteins of the same 

 name from different animal species have certain properties which dis- 

 tinguish them from each other. The serum-albumins can be crystal- 

 lized much more easily in some animals than in others. The same is 

 conspicuously true of the haemoglobins, which differ also in certain 

 animals in the relative proportion of sulphur and iron in the molecule, 

 as well as in the crystalline form. Even when no chemical or physical 

 differences have as yet been made out, proteins of the same name from 

 the blood or organs of different species show notable ' specific ' differ- 

 ences when subjected to certain biological tests (see, e.g., the paragraph 

 on Precipitins, p. 31 ; and that on Anaphylaxis, p. 32). 



Carbo-Hydrates. The most important carbo-hydrates in their physio- 

 logical relations are dextrose, levulose, galactose, lactose, maltose, 

 sucrose (cane-sugar), starch, and glycogen. As regards their chemical 

 constitution, the simplest carbo-hydrates are aldehydes or ketones 

 that is, the first oxidation products of primary and secondary alcohols 

 respectively. Thus dextrose is the aldehyde of sorbite, a hexatomic 

 alcohol (an alcohol containing six OH groups), while levulose is the 

 ketone of the isomeric alcohol called mannite, and galactose the alde- 

 hyde of the isomeric alcohol called dulcite. The sugars containing six 

 carbon atoms are termed hexoses. They include dextrose, levulose, 

 and galactose. The empirical formula of these three simple sugars (or 

 monosaccharides) is the same (CjHjaOg), but, owing to the different 

 arrangement of the atoms or groups of atoms, they have each their 

 characteristic properties by which they can be easily distinguished. 

 For example, dextrose rotates the plane of polarization to the right, 

 levulose to the left. By the union or ' condensation ' of two molecules 

 of a monosaccharide, with loss of a molecule of water, a disaccharide is 

 formed. Cane-sugar, maltose, and lactose, all with the same empirical 

 formula, (C^H^On), are disaccharides. Cane-sugar yields on hydro- 

 lysis a mixture of equal parts of dextrose and levulose ; lactose, a mix- 

 ture of dextrose and galactose ; while maltose is converted into dextrose. 

 By the condensation of more than two molecules of monosaccharide 

 polysaccharides are formed, such as starch, dextrin, and glycogen. The 

 exact molecular weights of these substances are unknown. Their 

 general formula can be written (C 6 H 10 O 5 ), where n represents the 

 number of monosaccharide molecules condensed to form the poly- 

 saccharide, in the case of starch probably some hundreds. 



Fats and Lipoids. The fats are compounds of higher fatty acids 

 with glycerin (glycerin esters). The ordinary body-fat consi:ts of a 



