MICROBE AND LIFE 



that can multiply in a simple medium composed of hydrogen, oxygen, 

 carbon dioxide, and minute amounts of some inorganic salts. By far 

 the majority of micro-organisms appears to represent types that form 

 a virtually continuous transition between these extremes. This im- 

 plies that various microbes exhibit diverse nutrient requirements for 

 the synthesis of proteins with which, as we know, life is associated. 

 Whether, as in the case of the hydrogen bacteria, the protein is manu- 

 factured from the above-mentioned simple ingredients, or, as in the 

 lactic acid bacteria, only from a complex mixture of protein degrada- 

 tion products, nevertheless the protein appears in every case to be 

 composed of practically the same building blocks, viz., the twenty-odd 

 amino acids that have also been found in the proteins of man, animal, 

 and plant. Nowadays this result tends to be accepted as self-evident; 

 yet, in view of the variety of processes that have been employed by 

 various organisms for the synthesis of their proteins, this could cer- 

 tainly not have been predicted. Once again we recognize in these facts 

 a most exalting demonstration of life's unity. 



And there is even more. Occasionally the nutrient requirements of 

 micro-organisms bear a special character; it was, for example, as- 

 certained that the addition of trace amounts of some cell extract to 

 an initially inadequate medium sufficed to permit the growth of an 

 organism. Continued investigations, in which our fellow-member, 

 Kogl, has had an important share, have shown that the special activity 

 of the cell extract was due to the presence of one or more organic 

 substances of relatively simple composition, and which in part govern 

 the life or death of an organism in astoundingly small concentrations. 

 As is known, a fully comparable situation is encountered in the nutri- 

 tion of man and animals, where extremely low concentrations of sub- 

 stances known as vitamins likewise determine the well-being of the 

 organism. But the most important point is the fact that in many cases 

 the identity of certain microbial growth factors with known vitamins 

 has been established. 



It is doubtful whether the significance of this discovery has been 

 fully appreciated. It is true that physiologists have gratefully taken 

 advantage of the opportunity to use micro-organisms as an aid in the 

 detection and quantitative estimation of the vitamins they were stud- 

 ying. The essential point is, however, the great general biological sig- 

 nificance of the concept that the nutrient deficiencies of man and 



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