8 



link themselves together to form structures, in some- 

 , what the fashion in which micells of cellulose are 

 joined together to form a cell wall. 



It is inconceivable how heredity or self-perpetuation 

 can be accounted for on the basis of anything except a 

 fibrous chemical structure, and since we know of at least 

 one crystalline or globular protein (tobacco leaf virus) 

 which does exhibit heredity and self -perpetuation, we are 

 compelled to assume that a fibrous chemical structure is 

 present in at least some of the globular proteins. 



s.^/ \/ N^^ 



hN Nh 



Double-strand polypeptide spiral. The diketopiperazine ring at the 

 upper end is in the process of assimilation, while the one at the lower end 

 may be considered as being in a state of temporary attachment to a pro- 

 teolytic enzyme. 



Every living organism is so constituted that growth by 

 assimilation of amino acid residues can take place inde- 

 pendently of other physiological processes. Since it must 



"O-C 



