298 PHYSIOLOGY FOR DENTAL STUDENTS. 



four fundamental tastes do not nearly represent all the 

 and flavors with which we are familiar. The relish of a tasty 

 meal, the piquancy of condiments, the bouquet of a fine wine, 

 would remain unappreciated were there no other nerve receptors 

 than those described above. Two other types of nerve receptor 

 are involved, namely (1), those of common sensation, as in the 

 case of acids, thus adding an astringent character to the sour 

 taste, and (2) those of smell as in the case of wines and flavored 

 foods. The importance of the sense of smell in "tasting'' ex- 

 plains the loss of this ability during nasal catarrh or cold in 

 the head. Under such conditions an apple and an onion may 

 taste alike. 



Certain drugs when applied to the tongue affect taste sensa- 

 tions in different degrees. Thus cocaine first of all paralyzes 

 the receptors of common sensation so that pain is no longer 

 felt and an acid loses all of its astringent qualities and merely 

 tastes sour. A little later the bitter taste also disappears, then 

 salt, then sour, but the saline taste remains even after the cocaine 

 has developed its full effect. Another interesting drug, acting 

 on the taste sensations, is a substance present in the leaves of 

 Gymnema sylvestre. After chewing these leaves, the aweet and 

 bitter tastes are absent, those of acid and of salt and ordinary 

 sensation (astringency, etc.) being, however, unaffected. 



The Sense of Smell. 



In man the sense of smell is very feeble when compared witli 

 that of lower animals, and it is of very unequal development in 

 different individuals. It is, moreover, readily fatigued, as is the 

 experience of every one who has been compelled to live in stuffy 

 rooms. The receptors are represented by the columnar epithelium 

 of the superior and middle turbinate bones and the adjacent 

 parts of the nasal septum. This epithelium is composed of large 

 columnar cells, each cell being connected with a nerve fiber which 

 is one of the branches of a fusiform bipolar nerve cell lying im- 

 mediately beneath the epithelium. The second branch of each 

 nerve cell runs through the cribiform plate to join the olfactory 

 bulb. After making connections with nerve cells here, the path- 



