PHYSIOLOGY OF OLFACTION 83 



represent the olfactory components that physiologists 

 have sought for so long. 



The very existence of partial anosmia implies olfac- 

 tory components the inactivity of one of which is ac- 

 countable for the partial defect. But such cases are too 

 little known to admit of clear interpretation. Thus 

 Aronsohn's observation (1886) that partial anosmia pro- 

 duced by the exhaustion of the nose through ammonium 

 sulphide leaves that organ sensitive to etherial oils but 

 insensitive to hydrogen sulphide, hydrochloric acid and 

 bromine, may be a differential effect between true odors 

 (olfactory endings) and irritants (trigeminal endings), 

 and not between groups of true odors. Nevertheless it 

 must be in this direction that an experimental analysis of 

 the general problem of olf action will eventually proceed. 



From this standpoint the condition presented by 

 mixed odors is of significance. At least two classes of 

 odor mixtures are to be distinguished, one spurious and 

 the other real. Spurious mixed odors are those in which 

 the gases or vapors act chemically on each other and thus 

 produce a third substance which may or may not have 

 an odor of its own. Thus ammonia and acetic acid both 

 stimulate the nose, but when mixed they possess no odor 

 for they combine to form odorless ammonium acetate. 

 Obviously such instances are not, accurately speaking, 

 instances of mixed odors. On the other hand there are 

 many pairs of odorous substances in which one member 

 does not act upon the other chemically and consequently 

 in which the two are left to act independently on the ol- 

 factory receptors. Such double stimuli, from the stand- 

 point of the component theory might be expected to excite 

 two sensations, but apparently this is not always the 



