Molds as Metabolic Models 89 



orientating force welding them into a discrete pattern; 

 that force is the doctrine of comparative biochemistry, pro- 

 mulgated in 1926 by Kluyver, in collaboration with 

 Donker. 



A corollary of this doctrine now has become a practical 

 working guide, that is, wherever a unique metabolic char- 

 acter is found, or a metabolic character is found in an 

 unusual degree, its study eventually is bound to have sig- 

 nificance transcending the organism originally studied. 

 It becomes, so to speak, a metabolic archetype, a metabolic 

 model. Herein lies the greatest virtue of the microbiologist 

 — he can pick his system. And so, to elucidate reactions 

 of broad biological significance, it has become the rationale 

 to select for study from the infinite variety available some 

 one or a few microorganisms that display the unique 

 intensity. 



Hhforical Sfudies on Fungi 



There is an ample number of such metabolic models 

 in the fungi, and I should like to select a few with which 

 to make special points. Historically, we may start at the 

 very beginning of experimental microbiology, namely, with 

 Pasteur. Having formulated the new concept of fermenta- 

 tion as a mode of respiration of brewer's yeast in the ab- 

 sence of oxygen, Pasteur became convinced of the broad 

 biological significance of this discovery only after showing 

 that various filamentous fungi behaved in the same way 

 as did yeast. In his famous "£tudes sur la Biere," pub- 

 lished in 1872, Pasteur wrote, ". . . . the study of varie- 

 ties of the genus Mucor, grown in natural or artificial 

 saccharine liquids, is of great importance to the establish- 

 ment of the physiological theory of fermentation. . . .** 

 Similarly, a subject of enormous importance nowadays in 

 biochemical genetics and in industrial microbiology is the 

 problem of the profound differences in metabolic behavior 



