28 WHAT IS LIFE ? 



The forces thus apparent are, however, dependent 

 on life. They are not exerted by the roots of dead 

 plants. The wick of a lamp sucks up oil only when 

 it is lighted, so that the fluid already absorbed is in 

 some degree removed, and thus capillary attraction 

 supplies what is lost by combustion. Just so, as the 

 plant exhales from the leaves, the endosmose will 

 keep up the supply ; but, let vitality be destroyed, 

 and absorption will cease. 



Organic bodies grow, therefore, not by the action 

 upon them of external agents, but by rendering 

 these subservient to their purpose. The primary 

 and leading feature of vitality is indeed the 

 process of nutrition ; and it can only be ex- 

 emplified by an organic being. Its first operations 

 appear in the alteration of the medium by which 

 it is surrounded. Oxygen is the great supporter 

 of life ; it is indispensable to the performance 

 of every vital operation ; deprived of it, organic 

 existence ceases, or is incapable of developing into 

 activity. 



In vain, however, do we ask, What is life ? If 

 we apply to chemistry, what do we learn from its 

 researches ? Only that the elements of organic 

 bodies are carbon, oxygen, hydrogen, azote, and 

 alkaline and earthy salts. Chemistry, potent over 

 the vast empire of inert matter, is unable to ascertain 

 what life is. Within its own dominions it can 

 analyze and combine ; make solids fluid, and fluids 

 solid ; resolve things into their elementary gases and 



