I. AVOID FRUITLESS EXPERIMENTS 21 



Auerbach, in investigating the production of chemical mutations b.y 

 the use of mustard gas, did not select a genetically unknown organism, 

 perhaps the tsetse fly, but chose the best known and most widely used 

 genetic material — Drosophila. His results were immediately com- 

 parable to similar effects produced by X rays and other mutagenic 

 agents. 



There is a rather obvious danger inherent in any unanimous choice 

 of a single organism for a given type of investigation. Important 

 discoveries are likely to be overlooked. For example, the guinea pig, 

 for which vitamin C is essential, stands almost alone among mammals 

 with respect to this nutritional characteristic. The discovery of the 

 vitamin nature of nicotinamide probably was long delayed because 

 rats only were used as the experimental material and most strains of 

 rats do not require it as a dietary ingredient. The later use of dogs 

 and monkeys led to the discovery. 



To avoid the systematic errors which may arise from the use of a 

 single biological material, diverse organisms must eventually be em- 

 ployed. Since many laboratories are not adequately equipped to 

 provide such broadened facilities, perhaps this later phase may be 

 done more conveniently elsewhere by some other worker. Many 

 confirmatory experiments are of this type. 



3. Select a Genetically Constant Organism 



The poet that rhymed: "A primrose by the river's brim, A 

 j^ellow primrose was to him. That and nothing more" was certainly 

 not deploring a lack of knowledge concerning the relative abundance 

 of its dominant versus recessive genes or to what extent the primrose 

 was homozygous for either. Much of the older biological literature 

 possesses dubious quantitative value owing to the fact that inadequate 

 control was maintained over the genetic constitution of the experi- 

 mental material. Workers in experimental biology today, however, 

 must become increasingly cognizant of the laboratory importance of 

 using organisms with known genetic constitutions. This point should 

 be stressed all the more in a book of this character since the physical 

 methods discussed may be employed by individuals not fully con- 

 versant with the biological variables. 



This genetic problem is relatively simple, though not always easy, 

 in the case of bacteria and other unicellular organisms since cultures 

 may readily be obtained from a single parent. In this manner one can 

 be assured that all of the organisms possess a common heritage. Even 



