28 WHAT IS LIFE 



matical theory. The nebular hypothesis has not done 

 so. It is on the defensive and has lost standing 

 during the past generation."^ 



In contrast: Mendeleeff observed periodicity of 

 qualities among the chemical elements, and arranged 

 his periodic table (1871), boldly describing elements 

 then unknown with which to fill gaps in it. The dis- 

 covery by others of the predicted elements furnished 

 superb proof of the correctness of his general inter- 

 pretation (and the interpretation of others) of the 

 phenomena. The progressive and periodic relation- 

 ship of the elements is an established fact on which 

 all later work upon atoms has thrown added light. 



Theodor Schwann announced his view that plants 

 as well as animals were constituted of cells. Experi- 

 ment soon established the correctness of his specu- 

 lation. 



Hans Driesch criticises the expression cell-" theory." 

 That organisms are built up of cells is, he explains, 

 "a simple fact of observation, and I therefore can- 

 not agree with the common habit of giving to this 

 plain fact the title of cell-' theory.' There is nothing 

 theoretical in it; and on the other hand, all attempts 

 to conceive the organism as a mere aggregate of cells 

 have proved to be wrong. It is the whole that uses 

 the cells .... or that may not use them: thus there 



* The Evolution of the Earth and its Inhabitants, 12. 



