410 ORGANS OF THE SENSES. 



yellow color in animals), the raucous surface changes its na- 

 ture : here (the upper part of the septum within, and the 

 two superior turbinated without), this membrane is much 

 less vascular, containing fewer glands and no vibratile cilia, 

 but having simply a columnar epithelium ; its characteristic 

 feature consists in the terminal branches of the olfactory 

 nerves, these fibres being so fine and so numerous that by 

 their presence alone an experienced histologist will recognize 

 a detached fragment of this olfactory membrane. These 

 nerve fibres appear to terminate at the surface by joining the 

 deep and slender extremity of the columnar epithelial cells ; 

 at all events, Schultze's researches seem to show that around 

 the epithelial cells of this region are found special organs 

 (olfactory cells of Schultze) or fusiform elements, elongated, 

 having a rounded protuberance in the middle with a nucleus, 

 the two extremities being prolonged in fibrilhe. The exter- 

 nal prolongation, which is the thicker of the two, passes be- 

 tween the epithelial cells to the free surface, while the 

 internal prolongation appears to continue with the fibres of 

 the olfactory nerve. This appears to be a well-established 

 instance of the relation between the nerves and the epithe- 

 lium, and it serves to explain the importance of the latter to 

 all the organs of the senses. 



The sense of smell is exercised either upon vaporous sub- 

 stances floating in the air, or imperceptible solid molecules 

 which the air carries along with it ; volatile bodies are, there- 

 fore, generally odorous. It has been observed that the sense 

 of smell is aided by moisture, and also that flowers are more 

 fragrant in damp weather than in dry. On the other hand, 

 if the quantity of vapor is too great, or if water is intro- 

 duced into the nasal chambers, the sense of smell is hindered, 

 or even ceases entirely, until the normal condition is restored 

 (the sense of smell is not so acute in foggy weather). 



The conditions under which vapors or odorous particles 

 must be brought in contact with the olfactory surface in 

 order to produce the necessary sensation are somewhat 

 peculiar and extremely restricted: they must be brought 

 by a current of air, and they can act only while this current 

 is in motion ; thus, if a piece of camphor is placed in the 

 nose while the air is quite still, no sensation is produced, and 

 the case is the same if the nasal chambers are filled with an 

 extremely fragrant volatile fluid. In order to smell perfectly, 

 therefore, we inhale the air by means of short successive in- 

 spirations. This is because, in the second place, the current, 



