THE SPACE RELATIONS TO ATOMS. 501 



Now as the only asymmetric atoms which have been 

 studied are C and N, and as N'" derivatives are included 

 in Exceptions II., we find that Exception IV., amounts to 

 the statement of the empirical law mentioned above, that 

 active bodies must contain an asymmetric atom, with the 

 addition that this atom must be C or N v ; it would seem, 

 then, that instead of saying asymmetric molecules are such 

 as contain AR'R"R"', etc., we must say asymmetric molecules 

 are such as contain CR'R"R"R 1V or NR'R"R'"R iv R v . This 

 remains to be proved ; but while insisting that the presence 

 of an asymmetric atom may not be necessary, it is fair to 

 emphasise the fact that, with the few exceptions of Class I., 

 it is sufficient to cause optical activity. 



This statement is at once demanded by theory and 

 warranted by observation. The number of derivatives of 

 N v which have been examined is not large enough to afford 

 a generalisation. It must suffice to say that activity un- 

 doubtedly exists among asymmetric bodies of this class. 



With asymmetric carbon compounds, however, the case 

 is very different. The proof of their activity has indeed 

 been complicated by the fact already mentioned, that active 

 molecules tend to form inactive aggregates. But this diffi- 

 culty, while it has delayed, has also confirmed the triumph 

 of the theory. The first method of splitting up the inactive 

 aggregate into active molecules {dedoub lenient t Activirung, 

 doubling), was discovered as long ago as 1848 by Pasteur, 

 who during the succeeding ten years originated the other 

 methods also. They are : — s 



I. Division by combination with other active molecules. 

 Thus by neutralising a solution of racemic acid with the 

 active alkaloid cinchonine, Pasteur was able to crystallise 

 out the salt of left-handed tartaric acid before its isomer, 

 and Ladenburg obtained coniine in active form by combin- 

 ing it with active tartaric acid. 



This method, however, is applicable only to acids and 

 bases. 



II. Division by the action of living organisms. Since 

 these are largely composed of active bodies (albuminoids, 

 sugars), this method may be regarded as a special develop- 



