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immediate precursor of indole. The latter conclusion is based on the 

 fact that if one of the tryptophan-deficient mutants is grown in the 

 presence of a minimal amount of tryptophan the mutant accumulates 

 anthranilic acid and excretes it in the medium from which it has been 

 isolated in the crystalline state. 



Here we have the interesting example of a biochemical mutant 

 forming a metabolic product quite unknown for the original type. 

 Is it not tempting to suggest in this connexion that the superiority in 

 penicillin production of several mutant strains of Penicillium notatum 

 obtained by radiation with X-rays or ultraviolet light, or by bombard- 

 ment with neutrons, is due to the inactivation of a gene determining 

 an enzyme by which in the wild strains penicillin is converted into 

 some other cell constituent? 



However this may be, it is not doubtful that the microbiologist of 

 the future will be able to produce microbes with potencies differing 

 markedly from those known up to this time. And the case of penicillin 

 and other antibiotics is there to testify that the production of even 

 minute quantities of metabolites with new properties may become of 

 far-reaching importance for mankind. 



Our conclusion then must be that the coming generations of micro- 

 biologists, far from being pitiable, will experience joys both from an 

 increased insight into the mysteries of microbial life and from an 

 increased mastery of its manifestations. And the industrial microbiol- 

 ogist will add one key industry to those already existing : the industry 

 in which microbes with desired qualities will be fabricated ! 



The lecturer is, of course, aware of the danger inhaerent in such 

 prophecies, and for this reason it seems high time to return to reality. 

 And then I think I may not conclude without devoting a few special 

 words to the progress made regarding our knowledge of that group of 

 micro-organisms which was nearer to Emil Christian Hansen's heart 

 than any others : the yeasts. It is in this domain that his name is right- 

 ly perpetuated in the generic names Hansenula and Hanseniaspora. 



If at this moment he could have been with us, what would he say? 

 Would he be satisfied with the way in which we his successors have 

 taken care of the heritage he left to us? 



After all that I have learnt about the character of this great scientist 

 I do not expect that he would be exuberant in his praise. It is well- 



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