26 THE FITNESS OF THE ENVIRONMENT 



Thus the microscope, with all its brilliant 

 contributions to knowledge of the form and 

 more gross structural elements of the cell, 

 hardly at all contributes to knowledge of its 

 physico-chemical organization as a mechan- 

 ism. Out of such needs a preliminary, if 

 very imperfect, rational description of proto- 

 plasm has arisen, and gradually the physical 

 and chemical laws governing protoplasm, its 

 form, composition, and stability, its con- 

 stituent parts and their mode of action, and 

 the physical and chemical changes within 

 it are being discovered. 1 The idea of dur- 

 able form in matter and energy that change 

 can now be applied to the cell with greater 

 advantage, in that descriptions of the form 

 and of the change are now at hand, though 

 as yet all too imperfect. 



Another profoundly important contribu- 

 tion of the science of metabolism to our 

 knowledge of the characteristics of life is the 

 discovery of the cycle of matter through 

 plants and animals. 2 The plant takes up 

 carbonic acid and water and a few other 

 simple substances from air and soil, and 



1 This subject is extensively treated by Hober, "Physik- 

 alische Chemie der Zelle und der Gewebe." Leipzig, 1911, 

 3d ed. 



2 This was originally clearly stated by Lavoisier. 



