g 2 THE SENSES 



Conical or Filiform Papilla. -^These, which are the most abundant 

 papillae, are scattered over the whole surface of the tongue, but especially 

 over the middle of the dorsum. They vary in shape somewhat, but for the 

 most part are conical. 



Taste Sensations. The occurrence of two kinds of special sensi- 

 bility, i.e., touch and taste in the same part, makes it sometimes difficult to 

 determine whether the impression produced by a substance is perceived 

 through the ordinary tactile sensitive fibers, or through those of the sense of 

 taste. In many cases, indeed, it is probable that both sets of nerve fibers 

 are concerned, as when irritating acrid substances are introduced into the 

 mouth. 



Many of the so-called tastes are due to the sapid substances being also 

 odorous, and exciting the simultaneous action of the sense of smell. This is 

 shown by the insipid taste of certain substances when their action on the 

 olfactory nerves is prevented by closing the nostrils. Many of the popular 

 drinks lose much of their apparent excellence if the nostrils are held close 

 while they are drunk. 



When these accessory sensations are taken into account it is found that 

 the clearly defined tastes are reduced to four: sweet, bitter, acid, and salt. 

 These taste sensations are produced by the respective substances when in 

 solution. If dry salt or quinine is placed on the surface of the tongue, no 

 taste appears until solution takes place in the secretions of the tongue. A 

 piece of metal, as a silver coin, gives rise to a seemingly distinct taste sensa- 

 tion, called metallic, but it is probably not to be accepted as co-ordinate with 

 the others. The acid taste may be excited by electricity. If a piece of zinc 

 be placed beneath and a piece of copper above the tongue, and their ends 

 brought into contact, an acid taste (due to the feeble galvanic current) is 

 produced. The delicacy of the sense of taste is sufficient to discern one part 

 of sulphuric acid in 10,000 of water, or one part of quinine in 200,000 of 

 water. But it is far surpassed in acuteness by the sense of smell. 



ACUTENESS OF THE SENSE OF TASTE. (HALL.) 



The average of 10 individuals. 



Sugar i part to 520 



Quinine i part to 444,000 



Acetic acid i part to 5,640 



Salt i part to 469 



Exploration of the taste areas reveals the fact that regions of the tongue 

 and mouth are not equally sensitive to the sapid substances. Sweet tastes 

 are especially developed at the tip and sides of the tongue, while bitter tastes 

 are almost absent in the front, but especially developed on the basal region, 

 and in the fauces and pharynx. Salts are more stimulating to the tip of the 

 tongue, and acids along the sides. Individual tests of the fungiform papillae 



