THE WONDER OF LIFE 473 



is surprisingly greater than that of our best engines. A 

 steam-engine, for the most part made of iron, is a material 

 system for transforming the potential energy of coal into 

 heat and work. A living organism, in great part built up 

 of proteids, carbohydrates, and other carbon-compounds, 

 is also a material system for transforming the potential 

 energy of food into heat and work. But the living organism, 

 considered as an engine, is much more effective than the 

 locomotive. For while the best steam-engine turns only 

 about twelve per cent, of its income of potential energy 

 into work ; the animal can give back as much as twenty- 

 five per cent. Moreover, the actual waste of heat in the 

 steam-engine is much greater than in the animal. 



We need not elaborate the contrast between living 

 creatures and engines. To any one bent on maintaining 

 that organisms are engines, we would point out that they 

 are self -stoking, self -repairing, self -regulating, self-adjust- 

 ing, self-resting, self-increasing, and self-reproducing 

 engines ! 



In his interesting book, The Cell as the Unit of Life, 

 Dr. Allen Macfadyen wrote : 



' A great part of physiological inquiry has consisted 

 in the examination and explanation, not of life but of the 

 mechanism of life, and so far as this mechanism is con- 

 cerned, adequate and satisfactory explanations have been 

 found in the ordinary laws of physics. It is when we come 

 to cellular activities that our real difficulties begin as regards 

 the essentially vital problems '. 



It is interesting to look up the works of Professor W. 

 Roux, a hard-headed anatomist and embryologist, the 

 pioneer in the modern study of ' developmental mechanics ', 

 to notice how constantly, in spite of that word ' mechanics,' 



