NEOPLASTIC ABNORMAL GROWTH 219 



progenitor. These qualities must depend upon some profound deviation 

 from the normal structure or function, or both. 



The distinctive characteristics of neoplastic grow^th are as striking as 

 those of the cells of the mutant bacterial colony described by Haddow 

 (4) : "The generation of a vigorously growing strain of bacterial cells 

 in a senescent colony presents a striking resemblance to the emergence 

 of a malignant variant in the cells of aging animal tissues." The com- 

 parison is supported by many examples of adaptive variations in bac- 

 teria. Here the cells of secondary colonies have been shown functionally 

 and structurally to be unlike the parents from which they arose, due to 

 the fact that they can metabolize constituents of the medium which the 

 progenitors are unable to attack at all. For lack of this competence the 

 parent cells, even though young and actively reproducing, are handi- 

 capped in their ability to carry on, with the substrate available, the meta- 

 bolic activities required for active proliferation. The variant, analogous 

 to the malignant cell, more versatile and perhaps better equipped bio- 

 chemically, can thrive under circumstances which are intolerable to its 

 less adaptable parent. 



The Control of Cellular Growth 

 AND Differentiation 



The role in cancer of a loss of the normal control of growth and dif- 

 ferentiation should be considered, whether or not we accept as correct 

 the conclusion that the constituent cell must involve something more 

 than a simple quantitative deviation of these factors from normal. There 

 are two possibilities : a wild growth, like that of cancer, might be due to 

 a local lack or a modification of some general control of development 

 and function; or, more possibly, the general force could remain un- 

 altered but be powerless to hold in restraint cells which have assumed 

 properties different from those of normal cells' properties through which 

 control is exerted under ordinary circumstances. Clearly, if a generally 

 applicable force has been modified to cause or to allow cancer to develop, 

 the modification must be one which afYects particularly a single specific 

 group of cells. It seems more probable that the cancer tissue has some 

 marked structural or functional difference from the normal, one which 

 should be detectable if searched for adequately. It is of the utmost im- 

 portance that any such difference be sought out and defined with the 

 greatest precision possible. 



Certain controls of differentiation exist which, if disordered, may 



