Genetic and Non-Genetic Variation 289 



aspects of drug application in medical therapy, this problem 

 is not especially relevant to understanding the origin of drug 

 resistance in vitro or in vivo. 



I apologize that most of this paper has been concerned with 

 semantic problems, since this is generally considered a most 

 boring subject in biology. However, I have followed a standard 

 practice in dealing with complex problems by constructing 

 a model. To place this model in its true perspective, the 

 reader is referred to a recent publication by two great scientists 

 on the use of models in biological research: "One well estab- 

 lished and generally accepted method of treating systems 

 which are complicated beyond comprehension is to construct 

 simple models and see whether they fit the systems in question. 

 If they do, you will immediately become suspicious, and so 

 will your colleagues most certainly, with the result that a 

 blooming literature springs up (or breaks out) dealing with 

 the problem of how you have managed to make all your 

 errors cancel one another. If they do not lit, the beauty of 

 the models themselves may shine for years untainted by the 

 squalid awkwardness of reality " (Fizz-Loony and Linderstrom- 

 Lang, 1956). 



REFERENCES 



Beale, G. H. (1954). The Genetics of Paramecium aurelia. Cambridge 



University Press. 

 Bertschmann, M. (1955). Z. indukt. Ahstamm.-u. VererbLehre, 87, 



229. 

 Clausen, J., Keck, D. D., and Hiesey, W. M. (1948). Publ Carneg. 



Inst., No. 581. 

 Delbruck, M., and Stent, G. (1956). In The chemical Basis of 



Heredity, p. 699. Ed. McElroy, W. D., and Glass, B. Baltimore: 



Johns Hopkins Press. 

 Demerec, M. et at. (1956). Publ. Carneg. Inst., No. 612. 

 Ephrussi, B. (1953). Nucleo-cytoplasmic Relations in Micro-organisms. 



Oxford University Press. 

 Fizz-Loony, F., and Linderstr0m-Lang, K. (1956). The Thermo- 

 dynamic Activity of the Male Housefly. New York: Academic 



Press. 

 Gale, E. F., and Davies, R., Ed. (1953). Adaptation in Micro-organisms, 



p. 69. Cambridge University Press. 

 Gale, E. F., and Folkes, J. P. (1954). Nature, LoncL, 173, 1223. 

 Gamow, G. (1955). Biol. Med., Kbh., 22, no. 8. 



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