CHAPTER III. 



PHYSIOLOGY OF OLFACTION. 



Contents.— 1. Nerves of Olfaction. 2. Passage of Air 

 through the Nasal Cavity. 3. Minimum Stimulus. 

 4. Physical Condition of Stimulus, Gas or Solution? 5. 

 Olfaction in Fishes. 6. Fatigue and Exhaustion. 7. Quali- 

 ties of Odors. 8. Chemical Relations of Odors. 9. Inade- 

 quate and Adequate Stimuli. 10. Oilfactory Reflexes. 

 11. Bibliography. 



1. Nerves of Olfaction. The olfactory region of verte- 

 brates has been shown to possess olfactory cells as ter- 

 minations of the olfactory nerve and free-nerve endings 

 representing in all probability the trigeminal nerve. It 

 has long been the opinion of investigators that the olfac- 

 tory sense is mediated by the endings of the olfactory 

 nerve, but this opinion has not been without its opponents. 

 Thus Magendie, in a series of publications beginning in 

 1824, came to the conclusion that the trigeminal nerve was 

 the nerve of olfaction and that the so-called olfactory 

 nerve was one whose function was wholly unknown. His 

 opinion was based in part upon experiments on the dog. 

 After the olfactory nerves of this animal had been cut, it 

 was found still to respond to acetic ether and to ammonia. 

 Even when blindfolded a dog with severed olfactory 

 nerves would seize cheese or meat but it would not eat 

 meat sprinkled with tobacco. It was pointed out by 

 Magendie 's critics that many of the stimulating sub- 

 stances used by him, such as ammonia and the like, not 



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