VARIETY OF VITAL ACTIVITY 101 



This strange instability, as of a fountain summit 

 or of a flame, is of the very essence of life and creates 

 the need for oxygen as well as the need for control. 

 If the demand or supply is small, the life will be 

 inactive ; if ample, vivacious ; if greater still, feverish. 

 At one end of life's scale we have the latent life of 

 seeds, the suspended animation of winter sleepers ; at 

 the other the consummation of a Shelley. Between the 

 two we have the periodic sleep and growth of plants, 

 the gradual rise of animal activity in water, on land, 

 and in the air, and the final achievement of permanent 

 activity of body and mind. 



Life, however, outruns our metaphors. In variety 

 of working, inwardness, and thrift it transcends our 

 figure of flame. Biological activity is not exhausted 

 by combustion. Muscle and nerve are most complex 

 tissues, and their inward changes are correspondingly 

 complex. Movement, whether of plant or animal, in- 

 volves a change of its electric tension which may be 

 too delicate for perception unless studied by a sensitive 

 electrometer, or so powerful (as in the torpedo or 

 electric eel) as to disable us. Nervous activity, again, 

 is akin to electric action. Even respiration is not 

 always the slow combustion we have described. A 

 molecular as well as a mass exchange of gases is known 

 in plants and animals. Leavening prepares for life. 



The inwardness no less than the variety of biological 

 action contrasts with our simple figure. A fire is an 

 affair of surface changes. Living things, on the other 

 hand, burn from within outwards. Fuel burns only 



