STEREO-CHEMISTRY AND PHYSIOLOGY 4 57 



An examination of the formulae shows that two conditions must 

 be fulfilled before the bacterium can act. In the first place, the 

 compound must contain a — CHOH— group next a — CH 2 OH 

 radicle ; and in the second place it must have a space formula 

 in which two hydroxyl groups lie next each other. In other 

 words, unless a compound contains the grouping 



H H 



I I 

 CH-OH-C C 



OH OH 



the bacterium cannot attack it. 



The foregoing results are sufficient to show that an intimate 

 relationship exists between the molecular configuration of 

 substances and the readiness with which they are attacked by 

 ferments. Since this relationship exists in these cases, it is 

 natural to expect a similar connection between the configuration 

 of a substance and its behaviour in the bodies of animals. A 

 large portion of all animal tissue is made up of asymmetric 

 substances, and it appears probable that if an optically active 

 substance is digested, either the dextro or the laevo form will 

 react more easily than its antipode during the process. 



When we consider the case of the three possible substances 

 (dextro, laevo, and racemic), and suppose for the sake of con- 

 venience that the dextro compound is more easily assimilated 

 than the laevo antipode by a given animal, we shall find that the 

 racemic substance offers a further peculiarity ; for if it passes 

 through the organism as an actual compound, both its com- 

 ponents will be destroyed to a certain equal extent, while if it 

 breaks down into a mixture of its constituents, the dextro form 

 will be attacked while the laevo isomer is unassimilated. We 

 shall meet several cases of this kind in the work about to be 

 described. 



The simplest case of all is that of the tartaric acids, which 

 has been described by Brion. 1 He found that racemic acid was 

 least oxidised in the animal organism ; next came dextro tar- 

 taric ; while laevo tartaric and meso tartaric were most strongly 

 acted upon. This proves that racemic acid, in its passage 

 through the organism, is not decomposed into a mixture of 

 dextro and laevo forms ; as in that case the laevo form would be 

 destroyed and a preponderance of the dextro form would remain. 



1 Brion, Zeit. physiol. C/iem., 25, 283 (1898). 



