636 SPECIAL SENSES 



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

 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 has been explained by the assumption that the olfac- 

 tory membrane gradually becomes accustomed to the odorous impres- 

 sion. This is an apparently satisfactory explanation ; for it can hardly 

 be supposed that the direction of the emanations, provided they come 

 in contact with the membrane, could modify their effects. In a 

 case of cancer of the stomach, with vomiting of fetid matters, the 

 patient at first perceived an offensive odor when the gases from the 

 stomach were expired through the nostrils ; but this gradually disap- 

 peared (Longet). 



Relations of O If action to the Sense of Taste. The relations of the 

 sense of smell to the sense of taste are very intimate. In the apprecia- 

 tion of delicate shades of flavor, it is well known that olfaction plays so 

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

 common practice of holding the nose when disagreeable remedies are 

 swallowed 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 impressions. 



It undoubtedly is true that the delicacy of the sense of taste is im- 

 paired when the sense of smell is lost. The experiment of tasting 

 wines blindfolded and with the nostrils plugged, and the partial loss 

 of taste during a severe coryza, are sufficiently familiar illustrations of 

 this. In the great majority of cases, when there is complete anosmia, 

 the taste is sensibly blunted ; 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 mem- 

 brane is not entirely insensible to special impressions. 



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

 phenomena that follow impressions made on 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 on animals. Other examples of the effects 

 of odorous impressions of various kinds are sufficiently familiar. 



According to Ferrier and others, the olfactory centre is on the 

 mesial surface of the brain, near the anterior extremity of the uncinate 

 gyrus ; but this location of the centre can not be regarded as definitely 

 determined. Stimulation of this part in monkeys produces peculiar 

 movements of the nostril and lip of the same side. 



