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bution of the olfactory nerves is much wider and the cerebral 

 development correspondingly greater in some animals than is 

 the case in man, where, however, the range of susceptibility 

 is wider. The variety of odors and the very minute quantity 

 of the substance required to produce smell are wonderful. 

 The most delicate analysis may fail to show traces of the sub- 

 stances which can be appreciated by the sense of smell. For 

 instance, 0.000000005 of a gram of oil of peppermint in 1 liter of 

 water can be detected. Some odors, like musk, are pleasant 

 perfume to some, while to others they are unendurable. The 

 acuteness of the sense of smell varies in different persons, and 

 this may apply to certain odors only. Like the sense of touch 

 and other senses, it can be developed by practice. Often in 

 cases of mental disease there are hallucinations of smell. 



The olfactory nerves arise from a mass of gray matter lying 

 beneath the anterior lobe of the brain upon the cribriform plate 

 of the ethmoid bone. This is the olfactory bulb, and is con- 

 nected by the olfactory tract with the cerebrum. Each olfac- 

 tory tract arises from the cerebrum by three roots, two of which 

 are composed of white matter and the third of gray matter. 

 By these it is connected with the olfactory centres. The per- 

 ceptions of the olfactory nerve and of the nerves of touch of 

 the nose often resemble each other, and some stimuli affect 

 both nerves. The common sensibility is evoked by such sub- 

 stances as are irritating or acrid ammonia gas has no odor, 

 but it stimulates the mucous membrane of the nose. The 

 relation between the two kinds of perception is lost, and the 

 smell of ammonia or of alcohol is spoken of when it is not 

 olfactory, but a sensory perception. 



Taste. The sense organs concerned in taste, the taste buds, 

 are located on the upper surface and sides of the tongue, the 

 anterior surface of the palate, and of the anterior pillars of the 

 fauces. Those of the posterior third of the tongue are connected 

 with the glossopharyngeal nerve, while those of the anterior 

 part of the tongue are connected with the lingual and chorda 

 tympani nerves. Taste perceptions are modified by simul- 

 taneous olfactory sensations, so that it is difficult to distinguish 

 between an apple and an onion when the nostrils are closed. 

 The intensity of taste increases ^with the area stimulated, and is 

 greatest when the stimulating substance is at the temperature 

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