THE SENSE OF SMELL. 



747 



From impressions truly olfactory it becomes necessary to dis- 

 tinguish the gustatory as well as tactile or irritative sensations upon 

 the nasal mucous membrane. The irritation and even pain produced 

 by the vapors of ammonia often lead it to be improperly classed as 

 "having a bad odor."- Experimentally, a dog with both olfactories 

 divided always starts from the odor of ammonia or of acetic acid. 

 This is due to painful stimulation of his Schneiderian membrane, 

 which gets its sensory nerve-filaments from the second branch of the 

 trigeminus. 



Uses. The organ of smell represents an advance sentinel for 

 the functions of respiration and alimentation. Among the lower 

 animals it serves for the recognition of sex. 



Fig. 306. Zwaardemaker's Olfactometer. ( TIGERSTEDT. ) (From 

 Tigerstedt's "Human Physiology," copyright, 1906, by D. Appleton and 

 Company. ) 



Hyperosmia and Anosmia. Hyperosmia, or increased sensitive- 

 ness of smell, is a common condition. It is very apt to be found 

 among the hysterical and in many other nervous disorders. Strych- 

 nine is one of the drugs which is capable of producing this condition 

 when it is applied locally in solution. 



Anosmia is a term used to designate a condition which is the 

 reverse of the beforementioned. It may be complete, when it is 

 usually congenital. In such a case the olfactory nerves are absent. 

 It is more usual, however, to find the condition partial Its causes 

 may be stenosis of the nasal cavities, disease of the olfactory mucous 

 membrane, or nervous diseases. Strychnine often relieves the con- 

 dition. 



The local application of a dilute solution of strychnia heightens 

 the sense of smell (hyperosmia). Smoking, the local application of 



