198 ELEMENTARY PHYSIOLOGY 



the cireumvallate papillae (Lat. circum, around ; and vallum, a 

 rampart) because they are each surrounded by a kind of wall or 

 rampart. 



All the papillae are richly supplied with blood-vessels and nerves. The 

 nerve fibres are obtained from two sources the glossopharyngeal and the fifth 

 pairs of cranial nerves. The former nerves supply the back of the tongue and 

 of the palate, while the latter send their fibres to the middle and tip of the 

 tongue. 



It is probable that both these nerves are nerves of taste, although they 

 appear to be dissimilar in their functions. It is easy to prove, for instance, 

 that different portions of the mucous membrane of the tongue and palate 

 possess different powers. Sweet and salt tastes are perceived more readily at 

 the tip than at the back of the tongue. Sugar may be brought into contact 

 with the back of the tongue or palate without any taste being detected, at least 

 until the tongue and the palate have been pressed together. Bitter tastes are 

 perceived best when applied to the back part of the tongue, and acids at the 

 edge. 



Fig. 1 80. Sectional View of a 

 FungiformPapma showing Y i8i.-Section of a Circumvallate 

 the arrangement of its Blood $^ 8howing ^ Di8tribution of 



vessels< its Nerve-Fibres. 



a, artery ; v, vein ; <r and d, capillary 

 loops ; e, epithelium. 



It appears that, in order to produce the sensation we call taste, 

 the particles of the substance tasted must come in actual contact 

 with the nerve-terminations of the mucous membrane ; that is, 

 they must penetrate the outer layer of the membrane which covers 

 the nerve-endings. Hence the substance to be tasted must either 

 be in solution, or must be capable of being dissolved in the saliva 

 or the mucus of the mouth, so that it may be easily absorbed. 



We must also remember that there is no sensation without the 

 brain that we do not taste a substance till the irritation of the 

 sensory fibres has been transmitted through these fibres to the 

 brain. 



Many of the sensations which we call taste or flavour are not simple but 

 very complex, in which both smell and touch play a very important part. 

 Smell is so closely associated with the sense of taste that the odour of a sub- 



