646 



THE SENSES 



mitral-cell layer. Among these cells run numerous fibers, chiefly from the 

 mitral cells and the fusiform cells of the glomerular layer. The general 

 arrangement is shown in figure 429. 



The Stimulation of the Olfactory Membrane. The extent of the 

 nasal mucous surfaces, and of the frontal and antral sinuses connected with 

 them, might suggest that the sensory olfactory surface is widely distributed, 

 but such is not the case. Air impregnated with vapor of camphor has been 

 injected into the frontal sinus through a fistulous opening, and odorous sub- 

 stances have been injected into the antrum of Highmore; but in neither case 



FIG. 429. Principal Constituent Elements of the Olfactory Bulb of a Mammal. (Van 



Gehuchten.) 



was any odor perceived by the patient. All parts of the nasal cavities are 

 endowed w r ith cutaneous sensibility by the nasal branches of the first and 

 second divisions of the fifth nerve, hence the sensations of cold, heat, itching, 

 tickling, and pain, and the sensation of tension or pressure in the nostrils. 

 That these nerves cannot perform the functions of the olfactory nerves is 

 proved by cases in which the sense of smell is lost, while the mucous mem- 

 brane of the nose remains susceptible to the various modifications of the 

 sense of touch. But it is often difficult to distinguish the sensation of smell 

 from that of mere feeling, and to ascertain what belongs to each separately. 

 This is true particularly of the sensations excited by acrid vapors in the nose, 



