SELECTED PAPERS 



crobes are potential competitors for the green plants which are the 

 basis of our food supply. Successful efforts have been made in this 

 country by Thaysen to arrive at an economically warranted produc- 

 tion of food yeast, and if at present the odds are still in favour of other 

 foodstuffs it does not seem unlikely that in a not too far future the 

 question: 'Yeast or meat, Madam?' will be quite commonplace in 

 restaurants. 



In comparison with yeast and similar micro-organisms the green 

 plants of our world crops are favoured by their photo-synthetical ca- 

 pacity which allows them to renounce organic nutrients, and to de- 

 pend on atmospheric carbon dioxide as their sole source of carbon. 

 For this reason it seems of great significance that the arsenal of the 

 industrial microbiologist has recently been reinforced by the addition 

 of some unicellular green algae, such as Chlorella vulgaris, which are 

 also equipped with a photo-synthetic apparatus. The future will teach 

 us whether a mass production of unicellular algae will prove to be a 

 remunerative proposition; the practical difficulties involved seem, in- 

 deed, to be considerable. The fact that under favourable conditions 

 Chlorella is potentially able to produce 4 tons of dry material per acre 

 in 8 days against only 1.5 tons of corn per acre in 90 days, gives a 

 ready explanation for the great interest of our American colleagues. 



Although at present the conditions for a wholesale production of 

 microbial cell material for the use of human or animal nutrition are 

 not yet fulfilled, nevertheless several microbes are now being cultiv- 

 ated in order to obtain some particularly valuable cell constituent 

 which, owing to its more or less complex configuration, is not easily 

 accessible by chemical synthesis. This holds unconditionally for var- 

 ious enzyme preparations which nowadays are produced on a con- 

 siderable scale, especially in the U.S.A., both from moulds and from 

 bacteria. Microbial preparations which bring about a hydrolysis of 

 starch, pectin or proteins have found wide application in several 

 industries. 



Another microbial product which on account of its complex con- 

 figuration does not need to fear competition from organic synthesis 

 has recently come to the fore. I refer to the bacterial polysaccharide 

 dextran, already mentioned in connexion with the sugar industry. Its 

 formation by the lactic acid bacteria is remarkable, because this 

 glucose polymer is only produced from saccharose, and not at al 



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