WHAT IS PHYSICAL LIFE 



in proportion to their number of explana- 

 tions, and as no demonstrated facts long 

 remain isolated in science, so one largely 

 accepted theory of the mechanism of 

 immunity, called Professor Ehrlich's side 

 chain theory, is found ultimately to have 

 important relations to our subject of cell 

 assimilation of food, or in other words, 

 how it is that food feeds us. It is difficult, 

 however, to lead the general reader along 

 the intricate lines of this hypothesis with- 

 out giving him a headache, and so we will 

 only attempt a necessarily imperfect out- 

 line of it, by beginning with a rough illus- 

 tration. If the reader has ever had the 

 pleasure, or to some the horror, of seeing 

 that fresh-water polyp called a hydra 

 f usca in a water receptacle which allows 

 him to be seen with a low magnifying 

 power, he then looks like a great octopus 

 swinging his ugly arms, all covered with 

 contractile nodules, about in the water. A 

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