kluyver's contributions to microbiology and biochemistry 



merely on the basis of a blind acceptance of the uncorroborated 

 claims of others, even if they were eminent authorities, was never a 

 Kluyverian attitude. Although deeply imbued with the overriding 

 significance of experimental data, he was prone to exhibit his pro- 

 nounced critical ability best when such results seemed to vitiate what 

 appeared to be a rational hypothesis on all other counts. And, just as 

 in the above-mentioned cases, a critical re-examination of the proper- 

 ties of yeast strains that had been reported to behave otherwise led to 

 an unexceptional confirmation of Kluyver's own findings. 



There was, however, no such basis for the belief that the fermen- 

 tation of maltose and lactose would be incompatible. Thus the rule 

 established could not lay claim to an expectation of general validity. 

 But at the time the literature contained no contrary reports and it was 

 in his own laboratory that the first examples of yeasts that can ferment 

 both maltose and lactose were discovered many years later, when 

 Kluyver and Custers [1940] investigated the yeasts associated with 

 'Iambic', a special product of the art of the Belgian beer brewers. To 

 date these Brettanomyces species still represent the only yeasts known to 

 possess this property, and the genus is defined partly on this basis. 



Finally the thesis contains information pertaining to two other 

 aspects of yeast physiology, viz., the fermentation of galactose, and 

 the problem of the relation between fermentation and assimilation of 

 various sugars. 



It had long been known that yeasts, although intrinsically able to 

 ferment galactose, sometimes do so only very slowly, or after pro- 

 longed periods of incubation. Various hypotheses had been advanced 

 to account for this phenomenon, and Kluyver conducted some crucial 

 experiments that supported the view that an adaptation process was 

 involved. It was found, for example, that a yeast suspension, prepared 

 from a culture in a galactose-containing medium, fermented galactose 

 about equally as fast as glucose. The most intriguing experiments 

 concerned with this problem were those in which it was demonstrated 

 that at 40°C, a temperature at which growth is precluded but glucose 

 fermentation is not affected, yeasts do not acquire the ability to ferment 

 galactose at all. This established the importance of some growth pro- 

 cess for the development of the new property. Kluyver considered it 

 likely that this would also be reflected in the new-formation of cells, 

 and carried out some experiments to test this. An appropriate yeast 



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