640 



PHYSIOLOGY 



The sense of taste, on the other hand, is used only for sampling the nature 

 of substances taken into the mouth and determining their ingestion or 

 rejection. It is therefore much simpler in its extent and more susceptible 

 of analysis. 



THE SENSE OF TASTE 



The end organs which subserve the function of taste are represented 

 by the taste buds. These are oval bodies (Fig. 317) embedded in the 

 stratified epithelium, which occur scattered over the tongue, a few being 

 also found on the hard palate, the anterior pillars of the fauces, the tonsils, 

 the back of the pharynx, the larynx, and the inner surface of the cheek. 

 On the tongue they are found chiefly in the grooves around the circumvallate 

 papillae of man, and in the grooves of the papillae foliatse of rabbits. A 

 few are also present on many of the fungiform papillae. They consist 

 of medullary and cortical parts, the former being composed of columnar 

 or sustentacular cells, the latter of thin fusiform cells, the taste cells 

 proper. The nerve fibres concerned with taste end in arborisations among 



these taste cells. The peripheral end of the 

 fusiform cell projects as a delicate process 

 through the orifice of the taste bud, so 

 that it can come in contact with the fluids 

 contained in the cavity of the mouth. A 

 sapid substance, to stimulate these organs, 

 must be in solution ; hence quinine in 

 powder is almost tasteless, owing to its 

 slight solubility in neutral or alkaline fluids. 

 DIFFERENTIATION OF TASTE. The 

 number of different tastes is very limited. 

 We distinguish four primitive taste sensa- 

 tions, viz. sweet, sour, bitter, and salt, 

 some authors adding to this an alkaline 

 taste and a metallic taste. Many sub- 

 stances owe their distinctive character when 

 taken into the mouth to the fact that they 

 stimulate not only the taste' nerves but 

 also the nerve endings of common sensa- 

 tion. Thus acids, when in weak solutioii, 

 have an astringent character besides their 

 sour taste, and if strong produce a burning sensation. The primitive 

 taste sensations can affect one another if excited simultaneously. 

 With weak stimulation one taste may practically annul another. Thus 

 a dilute solution of sugar is rendered almost tasteless by the addition to 

 it of a few grains of common salt. If the primitive taste sensations are 

 more strongly excited we get a mixed sensation, in which the components 

 can still be distinguished. Thus, adding sugar to lemon juice not only 

 diminishes its acidity but produces a mixed sensation, the quality of which 



FIG. 317. Two taste buds 

 from the tongue. 



e , Stratified epithelium ; 

 p, opening or pore of taste 

 bud ; s, gustatory cells ; 

 st, sustentacular cells. 



(K6LLIK KK.) 



