CARCINOGENESIS 



orderly and synchronous development of the metabolic patterns 

 just described, except that the inducing substances originate in 

 neighboring cells. 



It should be stressed that the competitive pathways leading 

 to reduplication or differentiation are in delicate equilibrium; 

 only slight shifts are required to divert them one way or the 

 other. Cell reduplication could be stimulated by any process 

 that diverts the cell food to the growth pattern. One way to 

 accomplish this is to inhibit one or more of the special functions. 

 Perhaps estrogenic hormones and croton oil stimulate mitosis in 

 this manner. In the presence of excessive demands on the 

 special functions, cell division would be retarded and hyper- 

 trophy result, whereas factors harmful to special functions 

 would stimulate growth and result in hyperplasia. 



On the basis of the evidence which engendered the dia- 

 grammatic scheme just presented, the following statements are 

 offered as a concept of normal growth : 



7. Normal primordial cells contain many potential mech- 

 anisms which ultimately determine differentiation. These 

 mechanisms become functionally active when the constituents 

 attain certain quantitative levels. 



2. During the process of growth and differentiation, all 

 living cells acquire or maintain certain biochemical processes or 

 metabolic patterns in common, but in addition each cell type 

 has special characteristic deviations from the general pattern, 

 resulting from variations in enzyme make-up. 



3. The specific cell pattern results from the deletion of 

 some of the mechanisms constituting the original make-up of the 

 cell and from the concomitant increase in other functions. 

 These losses and increases occur in a sequence which serves a 

 useful function and is beneficial to the general economy of the 

 organism. 



4. In normal cells the competing processes for reduplica- 

 tion and for special function alternate in dominance until the 

 final stage of maturation is reached. Then the pattern for 

 reduplication is irrevocably lost in some cells. 



687 



