STADLER 



ond step represents onlv^ an inference 

 that may later be modified or contra- 

 dicted by additional facts. When the 

 two steps are unconsciously combined, 

 we risk confusing what we know with 

 what we only think we know. 



The widely held belief that the fre- 

 quency of gene mutation may be 

 greatly accelerated by x-ray treatment 

 was an illusion of this kind. Its basis 

 was the use of the term gene 7initatio?i 

 with two distinctly different meanings. 

 Gene mutation was thought of as a 

 change in the constitution of a unit of 

 the genetic material, producing a new 

 gene with altered gene action. Gene 

 mutation was identified in experiments 

 by the occurrence of a mutant char- 

 acter inherited as if it were due to a 

 change in a gene. 



The mischief involved in the use of 

 the same term for the two concepts is 

 obvious. To insist that x-rays induce 

 gene mutation because the mutants in- 

 duced satisfy all the accepted criterions 

 of gene mutation, and that these mu- 

 tants represent qualitative changes in 

 specific genes because that is what we 

 mean by gene mutation, is to adopt 

 the dictum of Humpty Dumpty in 

 Through the Look'nig-Glass. "When 

 I use a word," Humpty Dumpty said, 

 "it means just what I choose it to 

 mean— neither more nor less." 



Now our concept of the gene is 

 entirely dependent upon the occur- 

 rence of gene mutations. If there were 

 no gene mutations, we could not iden- 

 tify individual genes, because the total 

 genetic effect of a single chromosome 

 would be inherited as a unit. If the 

 mutations we interpret as gene muta- 

 tions are in fact due to alterations 

 affecting groups of genes, then the 

 entities that we will recognize as genes 

 will be in fact the corresponding 

 groups of genes. The significant am- 

 biguity is not in our definition of gene 



249 



mutation but in our definition of the 

 gene itself, because any definition of 

 gene mutation presupposes a definition 

 of the gene. 



The discussion of these difficulties 

 and of the possibility of remedying 

 them by more rigorous definition of 

 experimental concepts is only an ap- 

 plication to biology of the operational 

 viewpoint that has become common- 

 place in modern physics, largely as a 

 result of the critical studies of P. W, 

 Bridgman {12). As Bridgman notes, 

 this sort of critical reconsideration, 

 made necessary in physics by the de- 

 velopment of relativity, is essential in 

 scientific thinking if the methods are 

 to be made elastic enough to deal with 

 any sort of facts that may develop. 

 The essential feature of the operational 

 viewpoint is that an object or phe- 

 nomenon under experimental inves- 

 tigation cannot usefully be defined in 

 terms of assumed properties beyond 

 experimental determination but rather 

 must be defined in terms of the actual 

 operations that may be applied in deal- 

 ing with it. The principle is not a new 

 one; it has been recognized, at least 

 implicitly, in the work of individual 

 scientists from an early period. Wil- 

 liam James stated it essentially in his 

 lectures on pragmatism {13), illustrat- 

 ing it with a quotation from Wilhelm 

 Ostwald: 



Chemists have long wrangled over the 

 inner construction of certain bodies called 

 tautomerous. Their properties seemed 

 equally consistent with the notion that 

 an instable hydrogen atom oscillates in- 

 side of them, or that they are instable 

 mixtures of two bodies. Controversy 

 raged but never was decided. "It would 

 never have begun," says Ostwald, "if the 

 combatants had asked themselves what 

 particular experimental fact could have 

 been made different by one or the other 

 view being correct. For it would then 



