THE BIOLOGY OF THE CELL SURFACE 



substituting a means of protoplasmic reactions for a non- 

 physical concept of molecules, we should be able to do what 

 so far has been attempted in vain in biology, namely, to 

 envisage differentiation and heredity as merely two expres- 

 sions of development. 



It has been said that differentiation of development 

 and genetics must remain forever separated.^ And when 

 and wherever geneticists have attempted a union of the 

 two, they have failed.- But since heredity is expressed 

 during the process of development and indeed is a kind of 

 differentiation, biology must attempt to find ground com- 

 mon to both. Up to now this common ground has not been 

 located. I here propose a suggestion concerning the role 

 of the gene in heredity and in differentiation. 



The moment that we postulate that differentiation dur- 

 ing cleavage turns upon the taking up of potencies leaving 

 free in the cytoplasm those that give the blastomeres their 

 characters as such, we see that an organ becomes such 

 because in the cytoplasm of its cells are those potencies free 

 which make it a special organ. Every cell in an organism 

 becomes what it is because its cytoplasm has free its par- 

 ticular potencies whilst its nucleus binds all others. These 

 latter would, if left unbound in the cytoplasm, act as 

 obstacles to the display of the special potencies. Thus, 

 the removal of potencies at the same time means removal 

 of obstacles to cytoplasmic reactions. 



My fundamental thesis is that all the differences, i.e., 

 differentiation, that appear during development, rest upon 

 cytoplasmic reactions. These are made possible through 

 removal of obstacles by nuclei, hence, by chromosomes and 

 genes. The nuclei by removal of substances release the 

 activity of the cytoplasm in one direction. The genes also 



^ Lillie, F. R., 192/, p. j6/. 

 - Morgafi; Golds chmidt. 



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