556 



PHYSIOLOGY 



fishes the olfactory lobes form the greater part of the higher brain, and 

 extirpation of them produces a loss of spontaneity and of delayed 

 reactions similar to that which can be brought about in higher types 

 by extirpation of the whole of the cerebral hemispheres. 



The sense of taste, on the other hand, is only used 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 repre- 

 sented by the taste-buds. These are oval bodies (Fig. 242) 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 papillse foliatse of rabbits. 

 A few are also present on many of the 

 fungiform papilla. They consist of medul- 

 lary and cortical parts, the former being 

 composed of columnar or sustentacular 

 cells, the latter of thin fusiform cells, the 

 taste-cells proper. The endings of 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 s'ight solu- 

 bility 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 



FIG. 242. Two taste-buds 



from the tongue. 

 e, Stratified epithelium ; 

 p, opening or pore of taste- 

 bud ; s, gustatory cells ; 

 st, sustentacular cells. 



(KOLLIKER.) 



