662 SPECIAL SENSES. 



be appreciated, it is almost unnecessary to state that the passage of odorous 

 emanations to this membrane by inspiring through the nostrils is essential 

 to olfaction, so that animals or men, after division of the trachea, being 

 unable to pass the air through the nostrils, are deprived of the sense of smell. 

 The act of inhalation through the nose is an illustration of the mechanism 

 by which the odorous particles may be brought at will in contact with the 

 olfactory membrane. 



It is a curious point, to determine whether the sense of smell be affected 

 by odors passing from within outward through the nasal fossae. Persons who 

 have offensive emanations from the respiratory organs usually are not aware, 

 from their own sensations, of any disagreeable odor. This fact is explained 

 by Longet on the supposition that the olfactory membrane becomes gradually 

 accustomed to the odorous impression, and therefore it is not appreciated. 

 This is an apparently satisfactory explanation, for it could hardly be supposed 

 that the direction of the emanations, provided they came in contact with the 

 membrane, could modify their effects. Longet has cited a case of cancer of 

 the stomach, in which the vomited matters were exceedingly fetid. At first, 

 the patient, when he expired the gases from the stomach through the nostrils, 

 perceived a disagreeable odor at each expiration ; but little by little this im- 

 pression disappeared. 



Relations of Olfaction to the Sense of Taste. The relations of the sense 

 of smell to gustation are very intimate. In the appreciation of delicate 

 shades of flavor, it is well known that the sense of olfaction plays so im- 

 portant a part, that it can hardly be separated from gustation. The 

 common practice of holding the nose when disagreeable remedies are swal- 

 lowed is an illustration of the connection between the two senses. In 

 most cases of anosmia there is inability to distinguish delicate flavors ; and 

 patients can distinguish by the taste, only sweet, saline, acid and bitter im- 

 pressions. 



It is undoubtedly true that the delicacy of the sense of taste is lost when 

 the sense of smell is abolished. The experiment of tasting wines blind- 

 folded and with the nostrils plugged, and the partial loss of taste during a 

 severe coryza, are sufficiently familiar illustrations of this fact. In the great 

 majority of cases, when there is complete anosmia, the taste is sensibly im- 

 paired ; and in cases in which this does not occur, it is probable that the 

 savory emanations pass from the mouth to the posterior portion of the nasal 

 fossae, and that here the mucous membrane is not entirely insensible to spe- 

 cial impressions. 



It is unnecessary, in this connection, to describe fully the reflex phenom- 

 ena which follow impressions made upon the olfactory membrane. The 

 odor of certain sapid substances, under favorable conditions, will produce an 

 abundant secretion of saliva and even of gastric juice, as has been shown by 

 experiments upon animals. Other examples of the effects of odorous im- 

 pressions of various kinds are sufficiently familiar. 



According to Ferrier, the olfactory centre is on the inner surface of 

 the anterior extremity of the unicate gyrus ; but this location of the centre 



