UNITY AND DIVERSITY IN THE METABOLISM 

 OF MICRO-ORGANISMS 



'My daughter Alice is a student in High School. One of the prescribed 



courses is General Science. The section on Bacteria left her with a vague 



impression of a world teeming with deadly germs awaiting an 



opportunity to infect mankind. It seems probable that 



this malignant conception of bacteria is very generally held. 



'In reality civilization owes much to the microbe.' 



(From the Preface of A. I. Kendall, ''Civilisation and the Microbe'. Boston, 1923) 



When, some time ago, I received the esteemed invitation to deliver 

 a lecture on some biochemical subject before the Netherlands' Chem- 

 ical Society, I gladly accepted because a true microbiologist may never 

 pass up the opportunity to contribute to the vindication of the smallest 

 living organisms. For there is an altogether too prevalent notion that 

 the microbes, as irreconcilable enemies of man, plant, and animal, 

 deserve attention only in order to make it possible the better to combat 

 them. However understandable such a concept may be in view of the 

 beneficial effects resulting from the brilliant discoveries of the role of 

 microbes in numerous diseases, it nevertheless does not detract from 

 the fact that it represents an extremely warped picture of reality. 



But I shall not use the time at my disposal to show you how, in a 

 microbe-less world, the conditions for human life on earth would 

 soon no longer be realized, so that man possesses at least as many 

 friends as enemies in the domain of the microbes. Taking advantage 

 of the fact that I am addressing a chemically trained audience, I shall 

 rather limit myself to an attempt at striking a sensitive chord by dis- 

 cussing the chemical potentialities of micro-organisms. I trust that a 

 sober review of these capacities may suffice to make you regard these 

 smallest living beings with a little more sympathy in the future. 



The most specific characteristic of living matter resides in its metab- 

 olic properties. It is an empirical fact that the maintenance of life re- 

 quires a continuous supply of special chemical substances which, in 



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