WHAT IS PHYSICAL LIFE 



But Darwin builded better than he 

 knew by making the food question such 

 a great one in the process of life, for 

 modern physiology has extended its scope 

 from the bodies of animals to each cell in 

 their bodies. In this undreamed of ex- 

 tension, Natural Selection is simply 

 swamped, or rather it is like emptying a 

 little brook into a sea. For now we find 

 that the different cells of the metazoic 

 body which had first given up their in- 

 dependence for interdependence, as we 

 have described, on the food question re- 

 assert their original autonomy. Every 

 cell of the body insists on having its own 

 diet. They all must have food or they 

 would die of starvation. They can grow 

 and be themselves in shape and in function 

 only according to what they feed upon. 

 But a muscle cell cannot live on what a 

 bone cell lives on, nor will the simple fare 

 which suffices for a cartilage cell be ac- 

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