SENSE OF SMELL. 845 



in the mucous membrane of the olfactory portion of the nose. Changes 

 there excited are conducted through the nerve-filaments to the brain, and 

 only then become recognized as the sensation of smell. 



It would appear that the sensation of smell is only developed on the 

 first contact of the odorous particles with the olfactory nerve, and, as a 

 consequence, in order to obtain an exact perception of delicate odors a 

 number of rapid inspirations are taken, the mouth being kept closed. 

 In this way the air is rarified in the nasal chambers and odorous parti- 

 cles stream over the olfactory region. Consequently, if we hold our 

 breath the sensation of smell ceases, even if we are in an atmosphere 

 impregnated with odorous substances. It is further stated that odorous 

 substances taken into the mouth and then expired through the posterior 

 nares produce no sensation of smell, possibly from the fact that in this 

 direction of the atmospheric current the particles are not brought into 

 contact with the olfactory region ; while, when bodies are inhaled with 

 the air through the nostrils, the current of entering air is broken up by 

 striking against the inferior turbinated bone, and part of the current 

 passes directly through the respiratory passages and part upward 

 through the olfactory region. 



The reason why odorous liquids placed in the nostrils are incapable 

 of affecting the sense of smell is perhaps to be explained by the action 

 of the fluid upon the olfactory cells, which perhaps possess a high degree 

 of imbibition and are paralyzed when brought in contact with large 

 quantities of fluid. Even water alone, as we know, will temporarily 

 arrest the sense of smell, and if the nostrils be filled with water some 

 time will elapse after the removal of the liquid before the sense of smell 

 is regained. 



The amount of substance which may be recognized by the sense of 

 smell is extremely small. Valentin has calculated that ^ro.irov.iHro of a 

 grain of musk may be recognized by the sense of smell. Even this is, 

 perhaps, an inside estimate, for a grain of musk will for years give 

 its characteristic odor to the atmosphere of a room, and the most deli- 

 cate balance will at the end of this time fail to recognize any reduction 

 in weight, and yet we are compelled to suppose that the odor has been 

 given to the atmosphere through the volatilizing of the particles of the 

 musk. 



As regards the sense of smell, all attempts to classify the impres- 

 sions which may be made upon it entirely fail. The only distinction 

 which can be made is into what are termed pleasant and disagreeable 

 odors, and yet, of course, these are simply relative terms. We may say 

 that a substance has the odor of turpentine or of roses, but this, of 

 course, gives us no means of classifying the causes of the sensations 

 produced. 



