Ill 



THE SENSE OF TASTE 133 



u\\ u. In all probability those organs are to some extent pre- 

 served, and the gustatory sensibility that Kiesow noted experi- 

 mentally in some adults and still more in infants may depend on 

 their presence. 



II. Physiological exploration, by means of solutions of the 

 ditl'erent sapid substances which are adequate stimuli of the 

 gustatory organs, is an even simpler method for determining 

 the topography of taste and an approximately exact localisation 

 of the taste-buds of the oral mucous membrane, but its application 

 offers not a few practical difficulties which may be removed by the 

 following precautions : 



(a) The gustatory mucous membrane of the oral cavity is also 

 provided with delicate sensibility for touch, temperature, and 

 pain. It is therefore necessary to select as stimuli specific 

 gustatory solutions of such constitution and temperature that 

 other forms of sensation are only slightly or not at all affected. 



(&) Many substances that seem to be gustatory are mainly or 

 exclusively olfactory ; we must consequently select as stimuli 

 such sapid substances as have no action upon the olfactory organ. 



(c) The great mobility of the tongue and the diffusion of the 

 substances applied to the surface of the buccal inucosa give rise 

 to errors in estimating the extent of a taste area. It is essential 

 that the subject should not move the part experimented on 

 before he perceives the sensation. It is further necessary to 

 distinguish the immediate and the delayed responses given by the 

 subject. The former prove that the part explored is really 

 gustatory, the latter are doubtful because the sensation may be 

 due to spread of the test substance. 



(d) It is possible that a given taste may be perceived in some 

 regions and not in others which none the less form part of the 

 gustatory area. It is therefore necessary to explore each part 

 methodically for each quality of elementary taste. 



Before so many precautions were taken gustatory sensibility 

 was usually attributed to almost the whole of the oral cavity and 

 a considerable portion of the pharynx. But when the above rules 

 were observed the extent of the gustatory area became restricted 

 by degrees to the limits now accepted by nearly all physiologists. 

 It cannot, however, be denied that there are divergences between 

 the different observers, which probably depend on individual 

 differences in the distril >ution of the end-organs of taste. 



In investigating gustatory sensibility it is usual to adopt either sapid 

 substances or the galvanic method. Aqueous solutions of sapid substances 

 are brought into contact with the oral cavity by means of small sponges 

 fixed to the end of a wooden or metal rod (Verniere, 1827). Soluble solid 

 substances may be applied directly by a brush (v. Vintschgau). When single 

 l>:i].ill;ie or inter-papillary spaces are to be tested all physiologists n<'\v 

 prefer Oehrwall's method, i.e. the use of tiny brushes with blunt points 

 .-.Unrated with the solution. In testing extensive surfaces diffusion oi 11 u id 



