PHYSIOLOGY OF OLFACTION 77 



for vanillin by smelling for a long time a pure solution 

 of this material. On testing now the solution containing 

 the mixture of substances, it was found to smell only 

 of cumarin. Thus the exhaustion of the olfactory sur- 

 face for vanillin did not prevent stimulation by cumarin. 

 The placing of these two substances in the same subdi- 

 vison is, therefore, obviously artificial. 



Similar evidence as to the artificiality of Zwaarde- 

 maker's classifications had also been obtained from the 

 study of persons suffering from partial anosmia and from 

 neither this line of investigation nor from that dealing 

 with partial exhaustion has there come any special jus- 

 tification of the conventional olfactory groupings. 



Yet it is admitted on all sides that olfaction is essen- 

 tially a chemical process. And, as a matter of fact, 

 some progress has been made in discovering relations 

 between chemical structure and olfactory sensation. 

 This isi not necessarily of a general nature, but seems/ 

 usually to be limited to narrow ranges. Thus among the 

 alcohols Passy (1892c) has discovered that the olfactory 

 potency increases progressively in passing over this se- 

 ries from methyl to amyl as shown in Table V. 



Ba,ckman (1917c) has likewise determined that ini 

 the methylbenzene series olfactory acuity for benzene, 

 toluene, xylene, cumene, and durene increases as the sub- 

 stitute methyl group increases. 



Changes in the quality of odors also follow some natu- 

 ral series of organic compounds as has been pointed out 

 by Hay craft (1900) in the following etherial salts. 

 Ethyl acetate with acetic etherial odor. 

 Propyl acetate with acetic odor and slight flavor. 

 Butyl acetate with slight acetic odor and pineapple flavor. 



