574 



COMPAKATIVE PHYSIOLOGY. 



PiQ, 



ing greatly assists the sense of smell. Again, if fluids, such as 

 eau de Cologne, he held in the nose, their aroma is not detected ; 



and immediately after water has 

 heen kept in the nostrils for a few 

 seconds, it may be noticed that 

 smell is greatly blunted. Such is 

 the case also when the mucous 

 membrane is much swollen from 

 a cold. There can be no doubt 

 that the presence of fluid in the 

 above cases is injurious to the del- 

 icate hair-cells, and that smell is 

 dependent upon the excitation of 

 these cells by extremely minute 

 particles emanating from aromatic 

 bodies. 



When ammonia is held before 



419.-En7.organ8 concerned in ^^^ ^^O^e, a powerful senSation is 



smell (after Kouiker). 1, from experienced : but this is not smell 



frog — a, epithelial cell of the ^ ™ , . » t 



olfactory area; s, olfactory cell, proper, but an atrection oi ordi- 



2, small branch of olfactory nerve ,. - j, .• i 



of frog, breaking up into a brneh nary sensation, owmg to stimula- 



Mii™f 'shlep*''^™' ^' ""^"^"^ tion of the terminals of the fifth 

 nerve. It is possible that the audi- 

 tory nerve may also participate, though certainly not so as to 

 produce a pure sensation of smell. 



Like the other sense-organs, that of smell is readily fa- 

 tigued ; and perhaps the satisfaction from smelling a bouquet 

 of mixed flowers is comparable to viewing the same, one scent 

 after another being perceived, and no one remaining predomi- 

 nant. 



Our judgment of the position of bodies possessing smell is 

 less perfect even than for those emitting sounds ; but we always 

 project our sensations into the outer world, never referring the 

 object to the nose itself. Subjective sensations of smell arc 

 rare in the normal subject, though common enough among 

 the diseased, as is complete or partial loss of smell. It has 

 been found that injury to the fifth nerve, interferes with smell, 

 which is probably due to trophic changes in the olfactory 

 region. 



Comparative. — The investigation of the senses in the lower 

 forms of life is extremely difficult, and in the lowest presents 

 almost insurmountable obstacles to the physiologist because 



