THE WONDER OF LIFE 487 



Powers of Life. Life is a powerful kind of activity. 

 We see this in many ways in the power of self-increase 

 that is so characteristic of living matter, one Infusorian 

 becoming a million in a week ; in the associated power 

 of transforming matter, the green plant changing air, 

 water, and salts into bread, the animal changing the plant 

 into flesh ; in the economical transformations of energy, 

 for as we have already mentioned, an organism considered 

 as an engine gives more return for the potential energy 

 supplied to it (the food or fuel) than any engine of man's 

 device ; in the capacity for storing potential energy without 

 much leakage, as we see so convincingly in the trees of 

 the forest ; in the manifoldness of the energy-transform- 

 ations that are accomplished, for we find one and the same 

 creature doing work, giving off heat, giving off light, and 

 exhibiting electrical changes ; in the exquisite responsive- 

 ness, for a sundew tentacle will detect the presence of a 

 minute drop of ammonium carbonate added to a large jar 

 of water, and the earthworm, though without ears, is aware 

 of the light tread of a thrush's foot. As it is impossible 

 to discuss all the powers of life, our method must be, as 

 throughout, only illustrative. We shall discuss two 

 powers or capacities as different as possible the power of 

 giving forth light, and the power of taking a rest in sleep. 



Luminescence. In illustration of the powers of life, 

 let us take the phenomenon of luminescence, or, as it has 

 been erroneously called, phosphorescence. From the 

 chemico-physical point of view, the organism is a material 

 system which effects the transformation of matter and 

 energy. It is the seat of continuous chemical changes 

 oxidations and reductions, hydrations and fermentations 

 which we sum up in the term metabolism. There is no 



