BUILDING OF LIVING MATTER 117 



Such molecules, like tiny magnetized iron 

 particles, can almost adhere together. 



This peculiar chemical body so evolved is 

 called an amino acid, and amino acids are 

 the basis for all the proteins. There are many 

 different types and thousands of individuals, 

 and these can build up a legion of protein 

 forms. It is most remarkable that here 

 also the peculiar property of the carbon 

 atom to be most stable in galaxies of six 

 again comes in. There are many exceptions, 

 but six is a very favourite number of atoms 

 for the amino acids to contain, and the 

 bulk of the mass of any protein mole- 

 cule is built up of amino acids with six 

 carbon atoms in the molecule, the hydrogen 

 atoms represented in the type formula shown 

 above, may be replaced by many diverse 

 groups, so swelling the host of individuals. 

 So long as there is an amino group and an 

 acid group the remainder may be arranged 

 on many schemes. 



Sometimes there are two amino groups 

 instead of one when the amino acid is called 

 a di-amino acid, also there may sometimes be 

 two acid groups. Some such di-amino groups 

 occur in all proteins. In the schematic 

 formulae, these di-amino acids furnish oppor- 

 tunities for branching or side-chains, so that 



