692 TEXT-BOOK OF PHYSIOLOGY 



of taste. The terminal branches, after entering the bud at its base, 

 develop fine tufts which come into contact with the cells. That the 

 taste-buds are connected with the nerves of taste is rendered probable 

 from the fact of their degeneration after division of the nerves. 



The Taste Area. The taste area, though confined for the most part 

 to the tongue, extends in different individuals to the mucous membrane 

 of the hard palate, to the anterior surface of the soft palate, to the uvula, 

 the anterior and posterior half arches, the tonsils, the posterior wall of 

 the pharynx, and the epiglottis. 



The Taste Sensations. The sensations which arise in consequence of 

 impressions made by different substances on the peripheral apparatus of 

 this area are in so many instances combinations of taste, touch, temperature, 

 and smell that they are extremely difficult of classification. Nevertheless 

 six primary tastes can be recognized : bitter, sweet, acid or sour, salt or saline, 

 alkaline and metallic. Though the contact of any bitter, sweet, acid, salt, 

 etc., substance with any part of the tongue will, if the substance be present 

 in sufficient quantity or concentration, develop a corresponding sensation, 

 some regions of the tongue are more sensitive and responsive than others. 

 Thus, the posterior portion is more sensitive to bitter substances than the 

 anterior; the reverse is true for sweet substances and perhaps for acids and 

 salines. 



The intensity of the resulting sensation in any given instance will depend 

 on the degree of concentration of the substance, while its massiveness will 

 depend on the area affected. 



THE SENSE OF SMELL 



The sense of smell is the sense by which certain qualities of substances 

 entering the nose are perceived. 



The physiologic mechanism involved in the sense of smell includes the 

 nasal fossae, the olfactory nerves, the olfactory tracts, and nerve-cells in those 

 areas of the cortex known as the uncinate convolution and anterior part of 

 the gyrus fornicatus. Peripheral stimulation of this mechanism develops 

 nerve impulses which, transmitted to the cortex, evoke the sensations of odor. 

 The specific physiologic stimulus is matter in the gaseous or vaporous state. 



The Nasal Fossae. The nasal fossae are irregularly shaped cavities 

 separated by a vertical septum formed by the perpendicular plate of the 

 ethmoid bone, the vomer, and the triangular cartilage. The outer wall 

 presents three recesses separated by the projection inward of the turbinated 

 bones. Each fossa opens anteriorly and posteriorly by the anterior and 

 posterior nares, the latter communicating with the pharynx. Both fossae are 

 lined throughout by mucous membrane. The upper part of the fossa is 

 known as the olfactory, the lower portion as the respiratory region. In the 

 former, the mucous membrane over the septum and superior turbinated 

 bone is somewhat thicker than elsewhere and covered with a neuro-epithelium 

 which constitutes 



The Peripheral End-organ. This consists of a basement membrane 

 supporting two kinds of cells, the olfactory and the sustentacular. The 

 olfactory cells are bipolar nerve-cells, the center of which contains a large 

 spheric nucleus. The peripheral pole is cylindric or conic in shape and 



