II. THE PATTERN OF PROTOPLASM 235 



The writer is unable, however, to find any firm reason for which 

 all the amino acids synthesized by organisms must be laevorotary. 

 Presumably some individuals of primeval primary organisms were 

 decomposed of L-amino acids, while at the same time the others were 

 of D-amino acids, but there could be any synergetic connection between 

 these two groups, as the one could not make use of the other because 

 of the principal difference in their crystal shape, so that there might 

 be a distinct line of demarkation, and perhaps an iron curtain hanged 

 between them as in the case of the two groups of man in the present 

 day. 



There are actually ample evidences showing that D-amino acids 

 are not only useless but sometimes injurious to the present-day L- 

 organisms. The inhibition of growth of both gram-positive and gram- 

 negative bacteria by D-amino acids has been well known (9) (10). 

 Especially D-serine appears to be injurious, as for example, the growth 

 of E. coli is injured even when D-serine is present in so small an 

 amount as 5 r per ml. (11). Furthermore, D-serine exhibits a nephro- 

 toxic action on rats (12). 



It has become evident that D-amino acids occur occasionally in 

 nature, particularly in products derived from certain molds and bac- 

 teria. Thus, D-proline occurs in a number of ergot alkaloids, ^whilst 

 several of antibiotics, particularly penicillin and gramicidin are notable 

 for their content of D-amino acid residues. In the case of penicillin, 

 the D-amino acid residue is one of critical structural features, since the 

 L-analog is without activity. The high molecular polypeptides in the 

 capusular substance of bacteria of the mesentericus group contains 

 also D-amino acids. 



It should be noted that all these substances are injurious to some 

 organisms, indicating evidently that optically different amion acids 

 are incompatible with each other. The supposed D-group of the or- 

 ganisms might have been extinguished by the injurious effect exerted 

 by some products of L-group, leaving the latter alone on the primeval 

 earth. If the L-group thus gained a victory over the D-group and left 

 alone, all the secondary organisms generated from them should also be 

 L-group and accordingly all the organisms have come to be L-group 

 without exception. It is supposed, however, that some L-organisms 

 existing at the present time have acquired the ability to synthesize 

 D-amino acids to exert injurious effects upon the rivals in order to 

 gain the victory in the struggle for existence. 



It has been shown that lactobacilli, which have lost the ability to 

 synthesize piridoxin, can grow in a medium which contains D-alanine 

 even in the absence of piridoxin. Organisms grown in this medium 

 are devoid of piridoxin and its derivatives, whereas organisms grown 



