STEREO-CHEMISTRY AND PHYSIOLOGY 465 



Hildebrandt,' examining ethyl, propyl, butyl, and iso-amyl 

 derivatives of benzyl-coninium iodide, found that the isomer 

 with the lower melting-point had also the weaker physiological 

 action. The general formula of these bodies is shown below, 

 the position occupied by the ethyl, propyl, butyl or iso-amyl 

 radicle being indicated by X. 



CH, 

 /\ 



CH.. CH., 

 I ■ I ■ 

 CH') CH — C3H7 



\/ 



I— N— CH, - C.Ha 



I 

 X 



In the preceding paragraphs we have shown that the influence 

 of the antipodic arrangement of atoms in a molecule is well 

 marked in many cases. We must now mention several instances 

 which show that differences in the configuration of compounds 

 may affect our senses. 



In the first place, we may point out that the crystals of the 

 dextro and laevo forms of sodium ammonium tartrate differ from 

 each other and from those of sodium ammonium racemate. 

 The optically active compounds crystallise in hemihedral form, 

 and the crystal of the d-sa.\t is the mirror-image of that of the 

 /-salt. The racemic salt exhibits no hemihedral faces in its 

 crystals. The spacial arrangement of atoms, since it lies at 

 the root of this difference in crystalline form, certainly affects 

 our sense of touch. 



Passing now to the question of smell, it has been found 

 by Werner and Conrad - that the methyl esters of the two 

 optically active trans-hexahydroterephthalic esters have different 

 odours; while Schmidt and Tiemann observed that racemic 

 terpenes were less odoriferous than the corresponding active 

 isomers. 



Taste, in its turn, is affected in the same way, for Piutti^ 

 states that the dextro and laevo forms of asparagine 



NH.,.CH,COOH 



I 

 CH3.CO.NH., 



' Hildebrandt, Ber., 38, 597 (1905). 



- Werner and Conrad, Ber., 32, 3052 (1899). 



3 Piutti, Compt. rend., 103, 134 (1886). 



