WILLIAM ROUX'S THEORY 167 



disposed side by side, like fragments of stone in a 

 mosaic, and destined afterwards to create the different 

 parts of the organism. This conception, which is in 

 contradiction to his main thesis, is not an integral part 

 of the organicist system. This system comprises two 

 theories which will be reviewed separately: the theory 

 of the struggle between parts and the story of func- 

 tional stimulation. 



The protoplasm of the cell is composed of chemical 

 molecules of various kinds which in the course of the 

 assimilation and disassimilation of the cell undergo 

 independent modifications. Nutritive fluids sur- 

 rounding the cell favour the multiplication of certain 

 categories of molecules, thus disrupting the equilib- 

 rium and allowing certain substances to predominate. 

 Likewise certain physical and chemical factors exert 

 their influence on substances which are not uniformly 

 sensitive to stimulation, those which react more 

 strongly undergoing more waste, and vice versa. 

 Substances whose assimilation is favoured, develop 

 more than others, but as space is limited (for the 

 capacity of the cell is limited), there arises between 

 them a competitive struggle in the course of which 

 some of them crowd the others out and, in the end, 

 predominate. The preponderance of certain sub- 

 stances, which are different in every cell (for their 

 initial conditions were different and the stimulation 

 was also different according to the location of the cells 



