iv THE SENSE OF SMELL 185 



state of anosmia was preceded by a brief period of hyperosmia. 

 Eeuter made a very interesting communication to the effect that 

 the anosmia produced by the action of cocaine is not only pre- 

 ceded but also followed by a period of hyperosmia, as the effect 

 of the cocaine is wearing off. Eollet then observed that on return 

 to the normal state after the action of cocaine there is a period in 

 which the liminal value oscillates considerably. 



Eollet further experimented with gymnemc acid and produced 

 a long period of total anosmia, after which he found that the 

 appreciation of single qualities of smell returned at unequal 

 intervals. 



From these observations as a whole it must be assumed that 

 the olfactory apparatus contains a certain number of component 

 elements (which are probably more numerous than those of taste) 

 endowed with specific sensibility to different elementary qualities 

 of smell. But in the present state of our knowledge this difficult 

 subject is far from being cleared up. 



VIII. In daily life, as in medicine and pharmacology, bad 

 smells are often corrected by other more pleasant odours. In 

 perfumery it is a common practice to mix different scents in 

 order to obtain pleasant olfactory sensations. To form a clear 

 picture of the effects of mixing different odours, or of their 

 simultaneous action on the two halves of the olfactory mucous 

 membrane, it is necessary to distinguish several possible cases. 



Sometimes on mixing odoriferous gases or vapours with other 

 gases new inodorous compounds are formed. Thus ammonia and 

 acetic acid form ammonium acetate, which has no smell. Accord- 

 ing to JSTagel an inodorous compound is also formed when the 

 smell of formaldehyde is counteracted by ammonia. Clearly in 

 these cases there is no physiological neutralisation of two olfactory 

 sensations. 



Again, the sensation produced by an unpleasant odour may be 

 succeeded by a stronger and more penetrating smell. In this 

 case the stronger smell alone excites our olfactory sense, but the 

 weaker does not disappear. It no longer excites the sense of 

 smell, either because its liminal value has been displaced, or 

 because attention is concentrated on the stronger odour. The 

 use of perfumes is generally directed to the disguising of bad 

 smells. Preparations of creolin or hypochloride of lime are used 

 to disguise the smell and disinfect the purlieus of public con- 

 veniences. Tar corrects the odour of ozoena, carbolic acid of 

 gangrene. Castor oil and cod-liver oil, which have for many 

 people an unbearable smell and taste, are made less unpleasant 

 by the addition of various substances. 



When two equally strong odours act separately on the two 

 nasal fossae, it is possible to perceive the one or the other odour 

 alternately. 



