PHYSIOLOGY OF OLFACTION 73 



associated ; the smell of illuminating gas was not a gen- 

 erally known odor till this material was brought into 

 common use. Should it be abandoned commercially, its 

 odor would cease to be a part of common human sensa- 

 tion. In consequence of economic changes many odors 

 of trade articles, of kitchen products, and the like have 

 disappeared from the list of human sensations and many 

 new ones have come in. Yet notwithstanding this rela- 

 tively rapid evolution in the field of olfaction, the organ 

 of smell seems to remain the same ; it gives up old forms 

 of stimulation and takes on new ones in a way that is 

 almost incredible. As a result of these peculiarities of 

 the olfactory organ the classification of odors has 

 proved to be a most perplexing problem and has 

 resulted in most instances in what seem to be extremely 

 artificial schemes. 



Haller and particularly Linnaeus proposed systems of 

 odors that have formed the bases for many of the modern 

 classifications such as the one given by Zwaardemaker 

 (1895). In this odors are arranged in nine general 

 classes each of which may contain two or more sub- 

 divisions. These nine classes are briefly as follows : 



1. Etherial odors ; three subdivisions : odors of fruits, 



beeswax, ethers. 



2. Aromatic odors ; five subdivisions : odors of camphor, 



cloves, lavender, lemon, bitter almond. 



3. Balsamic odors ; three subdivisions : odors of flowers, 



violet, vanilla, cumarin. 



4. Ambrosial odors; two subdivisions: odors of am- 



ber, musk. 



5. Alliaceous odors ; three subdivisions : odors of hydro- 



gen sulphide, hydrogen arsenide, chlorine. 



