232 C. p. RHOADS 



should happen to catalyze a reaction that improved the organism in 

 competition with its relatives the new reaction would be retained." 



The most dramatic experiments in support of this statement are those 

 of Lindegren {^2'). He studied the enzymes which ferment melibiose 

 and lactose as they are produced by yeasts of three strains and hybrids 

 between them. The enzymes are adaptive in character and appear, in a 

 genically qualified yeast strain, upon exposure to their respective sub- 

 strates. All segregants from heterozygous diploids carrying a single 

 pair of genes were able to adapt. Furthermore, two of the four adapted 

 melibiose-fermenting cultures lost the function when dissimilated, ade- 

 quate proof that the enzyme was transferred from the cytoplasm of the 

 heterozygous hybrid maintained on melibiose to the cytoplasm of segre- 

 gants which did not contain the gene. The enzyme was maintained in 

 these segregants as long as the sugar was present. The evidence is good 

 that the enzymes are self-perpetuating cytoplasmic entities, initiated by 

 genes, with levels independent of the gene but dependent on interaction 

 between the enzyme and the sugar. 



Unfortunately, all the genetic considerations of cell differentiation 

 as the result of mutations, either spontaneous or induced, are rendered 

 unsatisfactory by the fact that our knowledge of gene action is all de- 

 rived from organisms which reproduce sexually. Cancer cells are vege- 

 tative. Hence, if a consideration of variability and adaptation in other 

 forms has some pertinence to the cancer problem, we must examine the 

 facts regarding variations in other vegetative cells. Bacteria provide 

 such examples, and reveal again the fact that those agents which cause 

 mutations in sexual organisms susceptible to genetic study also cause 

 inherited alterations, usually toward losses in function, in vegetative 

 forms in which we have no way of demonstrating true genes, and are 

 active in the production of cancer. 



Bacterial Variation as Applicable to Abnormal 



Growth 



Pure cultures of microorganisms, like the tissues of the body, even 

 though they are derived from isolated single forms, are known not to 

 consist entirely of identical individuals. Under standard conditions 

 bacteria vary at a constant rate. If the variation provides the cell with 

 an advantage in its environment, the variant continues to multiply and 

 overgrows the cells of the type from which it arose. If it has derived no 

 advantage from the variation, it is overgrown and dies. Modifications 



