MECHANISM OF OLFACTION. 33 



of bone were discharged from time to time for three months 

 from openings in the posterior nares and the throat. He 

 was examined May 10, 1864 ; when the wounds had healed, 

 with falling in of the face over the left malar and nasal 

 bones. He had then entirely lost the power of distinguish- 

 ing odors. Upon applying acetic acid to the nostrils, he 

 stated that he felt a prickling sensation, but no odor. Dilute 

 ammonia produced a warm sensation. Chloroform gave no 

 sensation. He had no sensation from the emanations of 

 flowers. There was loss of general sensibility of the nasal 

 mucous membrane on the left side, with diminished sensibility 

 on the right side. He had a sensation, not very definite, 

 when in water-closets, where (as he was told) the odor was 

 very offensive, but experienced no sensation, unless the ema- 

 nations were very powerful. Before entering the army, he 

 was a photographer by trade, and was familiar with the odors 

 of acetic acid and ammonia. In this case, it is almost certain 

 that the olfactory nerves had been divided, though other in- 

 juries undoubtedly existed. 



Mechanism of Olf action. 



There can be no doubt at the present day with 'regard to 

 the mechanism of the sense of smell. Substances endowed 

 with odorous properties give off material emanations, which 

 must come in contact with the olfactory membrane before 

 their peculiar odor is appreciated. As we have seen, this 

 membrane is situated high up in the nostrils, is peculiarly 

 soft, is provided with numerous glands, by the secretions of 

 which its surface is kept in proper condition, and possesses 

 the peculiar nerve-terminations of the olfactory filaments. 



In experimenting upon the sense of smell, it has been 

 found quite difficult to draw the exact line of distinction be- 

 tween impressions of general sensibility and those which at- 

 tack the special sense ; or, in other words, between irritat- 

 ing and odorous emanations. Undoubtedly, the vapors of 

 ammonia, acetic acid, nitric acid, etc., possess irritating prop- 



