CARCINOGENESIS 



during which the autonomous mass invades and metastasizes. 

 Usually it is not until this last stage that cancer is clinically 

 recognizable. The three periods are illustrated in the experi- 

 ment in which tumors are initiated in the skin of mice by a single 

 application of a carcinogenic hydrocarbon and promoted to an 

 autonomous cluster of cells by the frequent applications of 

 croton oil (9,56,57). The autonomous mass then grows and 

 invades the adjacent tissues in the absence of inciting agents. 

 Other examples of the prolonged process of cancer formation 

 are presented in papers by Blum (11), Furth (22), and Gardner 

 (24). 



On the basis of hundreds of experiments on the subject of 

 cancer and ancillary fields, it is now possible to present a sim- 

 plified diagrammatic picture of the factors which control the 

 reduplication and specialization of cells and to indicate how this 

 normal pattern can be altered during the formation and sub- 

 sequent growth of neoplasms. Although the concept to be 

 presented takes root from such facts, it must be admitted that it 

 is partly speculative, and one should not be deluded with the 

 belief that the picture is complete or perfect. One reason for 

 presenting this concept is the hope that it may suggest further 

 experimentation. Normal growth and differentiation will be 

 considered first. 



Normal Growth 



For the purposes of the present paper all cellular functions 

 are divided into two chief categories: one, the function of 

 reduplication, and two, all other special functions not primarily 

 concerned with cellular multiplication. The following pres- 

 entation is based on the concept that the process of cell redupli- 

 cation and the special functions interact in two distinct ways. 

 In addition to being mutually dependent, these functions must also 

 be recognized as mutually competitive with respect to the available 

 cellular nutrients. Thus, the development of cells is a resultant 

 of the outcome of the dynamic balance between cell reduplica- 

 tion and special function. 



681 



