476 THE WONDER OF LIFE 



particular reaction, and it is the same in the eagle as in the 

 test-tube ; but the riddle of life is that of the burning 

 bush — nee tamen consumebatur. 



The Power of Growing. — Given a material system 

 that could balance accounts, that did not simply run down 

 briUiantly and fizzle out, hke the flaring pill of potassium 

 thrown on the basin of water, the logically second criterion 

 is growth or self-increase. A surplus of income over 

 expenditure, that is the primal condition of organic growth 

 (for crystal growth and osmotic growth is not relevant at 

 all) ; the essential criterion is that out of material quite 

 different from itseK the living creature is able to meet not 

 only current expenditure, but to lay by something — ^for 

 growth. That income should exceed expenditure is the 

 obvious condition of organic growth. 



The Capacity for Behaviour. — The growth of an 

 organism impHes an active assimilation, not a passive 

 accretion, but it makes more venturesome activity possible. 

 Having some reserves in hand is one of the conditions of 

 agency. In some of the simplest organisms it has been 

 observed that movement stops when certain substances 

 included in the hving matter are used up, and does not begin 

 again until they are replaced. They are among the con- 

 ditions of behaviour, just as food and water are among the 

 conditions of the continued progress of a band of explorers. 

 But the hfe is more than meat. 



When we study the activities of the very simplest 

 organisms we do not find that they are simple. The move- 

 ments of advance and retreat and re-advance exhibited 

 by some of the mysterious slime-fungi (Myxomycetes) are 

 beyond any re-description in terms of present-day chemis- 

 try and physics. They exhibit the rudiments of behaviour. 



