44 ORIGIN AND NATURE OF LIFE 



a loose or labile equilibrium of periodic 

 building up and breaking down in rhythmic 

 flow all through life. Now, as this living cell 

 grows in size there appears to develop a higher 

 potential, or pressure of energy, of its own 

 peculiar type, which renders the cell unstable 

 also, and by the establishment of what are 

 known as dynamic centres, a play of energy 

 transformations starts, causing the cell to 

 divide and give rise to two daughter cells, 

 which are at first stable in balanced equili- 

 brium, and only by growth and accumulation 

 of energy-pressure later reach a stage at which 

 they, too, become unstable and again divide. 

 Also, in a complex many-celled organism, 

 there are groups of cells much like the periodic 

 groups of the chemical elements. Some cells 

 are permanent or stable, and do not divide 

 throughout life, at any rate after the full 

 size of the individual of which they form a 

 constituent part has been attained. Their 

 period of stability is the same as that of the 

 whole animal. Other cells are most unstable, 

 with energy content reaching a maximum 

 and leading to cell-division at frequent 

 intervals ; such cells as these are many times 

 formed, and perish, in the life of the animal. 

 Incidentally it may be pointed out that 

 it is this varying stability which determines 



