CH. V.] 



ASYMMETRIC COMPOUNDS. 



151 



atom attached to four different groups is known as an 

 asymmetric carbon atom. The possession of an asymmetric 

 carbon atom in a compound is essential to the possession 

 of optical activity by that compound. 



If equal parts of the d- and /- varieties of a compound 

 be mixed together, the solution of the substance is "opti- 

 cally inactive by external compensation." Such an in- 

 active mixture is known as "racemic," and is designated 

 by dl- or i-. When a compound that contains an asym- 

 metric carbon atom is synthesised, it is always found that 

 equal parts of the d- and /- varieties are formed. These 

 can often be resolved into their active constituents by 

 various methods, the most interesting of which is the 

 biochemical, depending on the property of living organisms 

 of selective assimilation, one of the two components being 

 destroyed more rapidly than the other. A few examples 

 of this are given below. 



This power of selective assimilation finds a parallel in 

 the different physiological action of enantiomorphs on the 

 body, and of the body and also of enzymes on enantio- 

 morphs. For instance, ^/-adrenaline has only slightly 

 more than one-half the physiological activity of the natural 



