472 THE WONDER OF LIFE 



opportunities of enjoying the observation of life as it is 

 lived in Nature, would be unanimous in admiration of 

 every living creature. The normal outlook, admittedly 

 difficult to attain to, is expressed in Walt Whitman's well- 

 known creed : 



4 1 believe a leaf of grass is no less than the journey- work of the 



stars, 

 And the pismire is equally perfect, and the grain of sand, and the 



egg of the wren, 



And the tree-toad is a chef-d'oeuvre for the highest, 

 And the running blackberry would adorn the parlours of heaven, 

 And the narrowest hinge in my hand puts to scorn all machinery, 

 And the cow crunching with depressed head surpasses any statue, 

 And a mouse is miracle enough to stagger sextillions of infidels.' 



Organisms and Mechanisms. Both in teaching and 

 in investigation it is very useful to compare living creatures 

 to engines. Both are material systems for the transforma- 

 tion of matter and energy. But the analogy is most 

 useful when it breaks down, for then the insignia of life 

 stand out in relief. Professor Joly long ago pointed out one 

 of the deep differences between an inanimate material 

 system and a living organism : 



' While the transfer of energy into any inanimate material 

 system is attended by effects retardative to the transfer 

 and conducive to dissipation, the transfer of energy into 

 any animate material system is attended by effects con- 

 ducive to the transfer and retardative of dissipation '. 



Charging a Leyden jar or heating a bar of iron is attended 

 by effects very different from those which attend the 

 feeding of an animal. 



But without dwelling on this technical difference, though 

 it seems to us far-reaching, we may emphasize the fact that 

 the efficiency of the living creature considered as an engine 



