132 LIFE: ITS NATURE AND ORIGIN 



upset (e.g., inversion, translocation, crossing over) which places 

 the gene in different surroundings (position effect). If heritable 

 and non-lethal, both these types of change generally lead to new 

 mutant forms of plants or animals. The modification of enzymes 

 within a cell, or the formation or introduction of new enzymes 

 there, could lead to catalytic variations of chemical output which 

 might simulate the effects producible by a point or a chromosomal 

 mutation; but the result would be transient unless sufficient of 

 the modifiers and prosthetic groups to maintain it were supplied 

 or produced. Another possibility is that a specific area may serve 

 as a template or mold against which may be formed specific cata- 

 lytic molecular structures or plaques. Still another possibility is 

 the local establishment of ionic or trace-substance conditions 

 favorable to the formation of new enzymes, e.g., by adsorptive 

 fixation of a prosthetic group by a carrier. Viruses and bacteri- 

 ophages reproduce themselves in cells, thus (where they exert 

 catalytic action) behaving as if they were free-living genes. What 

 is said of genes may be applied with equal force to mitochondria; 

 for whether these are symbionts or cytoplasmic inclusions, they 

 apparently reproduce and are efficient in directing chemical 

 changes within the cell (either directly or through enzyme forma- 

 tion), and behave somewhat as if they are free-living genes or gene 

 groups. 



The stability of genes and the efficiency of the protections sur- 

 rounding them are evidenced by the regular and orderly sequences 

 normal to life, which shows that gene mutations are relatively 

 quite rare, and abnormal gene or catalyst modifications unusual. 

 Since non-lethal gene mutations may be transmitted by heredity, 

 they are basic factors in evolution; for beneficial mutations tend 

 to survive and dominate, whereas harmful ones tend to die out. 

 If mutation makes a gene (or other catalyst) more susceptible to an 

 abnormal modification, that is one way in which the effect of a 

 mutation may become evident. 



Bacterial Dissociation and Transformation 84 



The colonies of most bacteria that have been studied may 

 appear in a rough, corrugated form (R), or in a smooth, glistening, 

 drop-like form (S). The change of a culture from R to S, or vice 

 versa, is known as dissociation. The methods used to produce 

 dissociation involve, mainly, change in the usual growth medium: 

 (1) by the addition of sera, normal or immune; (2) by addition of 



