SENSATIONS OF SMELL AND TASTE 499 



that which can be brought about in higher types by extirpation of the who] 



of the cerebral hemispheres. 



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

 of substances taken into the mouth and determining their ingestion or re 

 jection. 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. 244) 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 foliatae 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 FlG> 2 44. TWO taste-buds 

 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. 



The number of different tastes is very limited. 

 We distinguish four primitive taste sensations, viz. sweet, sour, bitter, 

 and salt, some authors adding to this an alkaline taste and a metallic taste. 

 Many substances 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 sensation. Thus acids, when in weak solution, 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 taste- 

 less 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 distingushed. Thus, adding sugar 

 to lemon juice not only diminishes its acidity but produces a mixed sensa- 

 tion, the quality of which is pleasant and in which the components, sour and 

 sweet, can be easily distinguished. We get no such fusing of sensations 



from the tongue. 



bud ; s, gustatory cells; 



st > 



