CHARACTERS OF LIVING MATTER 9 



kind of growth, however, is not due to assimilation, 

 but to chemical affinity by which the atoms of 

 different elements select or have a preference for 

 the atoms of other elements, in the way that one 

 atom of nitrogen is capable of combining with three 

 atoms of chlorine and thereby forming a molecule 

 consisting of four atoms. Side-chains and rings are 

 formed by materials which have a similar affinity ; 

 two molecules may be united to form a more complex 

 molecule ; by such a process growth may be said to 

 occur. In a similar way change sometimes takes 

 place within a molecule by a rearrangement of the 

 atoms within it ; no loss or addition occurs in such 

 an arrangement ; the same number of atoms of the 

 same element exist in the molecule, but their position 

 is changed, as when ammonium cyanate becomes 

 converted into urea. 



CH 4 N 2 0=CH 4 N 2 i.e. CN'ONH 4 becomes CONH 2 'NH 2 . 



Ammonium Urea 



cyanate 



The Atomic doctrine of Democritus was accepted 

 wholly or in part by most of the philosophers of the 

 Renaissance and their successors until Dalton formu- 

 lated his law of multiple proportions, which conferred 

 upon the theory of atoms a new significance. This 

 doctrine still stands firm, although there have been 

 notable secessions from it ; without this fundamental 

 conception of matter, a theory of the material universe 

 is almost impossible. The idea of gravitation and 

 the polarity of magnetism has induced in the minds 

 of some ardent thinkers and observers " the concep- 

 tion that atoms and molecules are endowed with 

 attractive and repellent poles, by the play of which 



