80 SMELL, TASTE, ALLIED SENSES 



groups (Fig. 18g) are attached so as to represent both 

 the para-position (spicy) and the ortho-position (flow- 

 ery). By this ingenious system Henning has attempted 

 to connect odor with chemical constitution and though 



FIG. 18. Generalized diagrams of the molecular structure of the six classes of aromatic 

 bodies that serve as olfactory stimuli according to Henning (1916) ; a, for spicy odors; b, for 

 flowery odors; c, for fruity odors; d, for resinous odors; e, for burnt odors; f, for foul odora; 

 and g, for an intermediate odor between spicy and flowery. 



the attempt is avowedly fragmentary and may be open 

 to much subsequent modification, it gives promise of 

 the solution of a problem that heretofore has been 

 most baffling. 



9. Inadequate and Adequate Stimuli. Inadequate 

 olfactory stimuli are apparently very few in number and 

 not well known. Thermal stimuli when applied to the 



