SMELL AND TASTE 1037 



tometers. Zwaardeinaker's olfactometer consists of a piece of india- 

 rubber tubing fitted inside a glass tube, through which air is drawn 

 into the nostrils. Another glass tube just fitting the rubber tube is 

 pushed inside it, so as to cover a portion of it. The minimum amount 

 of surface of the indiarubber tube which must be left exposed so that 

 the smell of the rubber may be perceived is a measure of the acuteness 

 of smell. To investigate other odours tubes of the corresponding 

 odorous substances can be constructed. 



Taste. The sense of taste is not so strictly localized as the sense 

 of smell. The tip and sides of the tongue, its root, the neighbour- 

 ing portions of the soft palate, and a strip in the centre of the dorsum, 

 are certainly endowed with the sense of taste; but the exact limits of 

 the sensitive areas have not been denned, and, indeed, vary in 

 different individuals. 



The nerves of taste are the glosso-pharyngeal, which innervates the 

 posterior part of the tongue, and the lingual, which supplies its tip 

 (see p. 896). The end-organs of the gustatory nerves are the taste- 

 buds or taste -bulbs, which stud the fungiform and circumvallate 

 papillae, and are most characteristically seen in the moats surrounding 

 the latter. They are barrel-like bodies, the staves of the barrel being 

 represented by supporting cells; each bud encloses a number of gusta- 

 tory cells with fine processes at their free ends projecting through the 

 superficial end of the barrel. They are surrounded by the end arboriza- 

 tions of the fibres of the gustatory nerves. Taste-buds are also found 

 on the posterior surface of the epiglottis and in the larynx. It has 

 been suggested that these form the afferent end-organs of a reflex 

 apparatus which guards the glottis against the entrance of food in 

 deglutition (Wilson). Epithelial buds, different from the olfactory 

 elements, also occur in the olfactory region of the nasal mucous mem- 

 brane. It is possible that the so-called nasal taste e.g., the sweet 

 taste caused by chloroform when aspirated in not too small an amount 

 through the nose depends upon these buds. 



A to the properties in virtue of which sapid substances are 

 enabled to stimulate the gustatory nerve- en dings, we know that 

 they must be soluble in the liquids of the mouth, and there our 

 knowledge ends. An attempt has been made by various authors 

 to connect the taste of such bodies with their chemical composition, 

 but researches of this kind have not hitherto yielded much fruit. 

 The number of distinct qualities of taste sensation is considerable, 

 but by no means so great as the number of qualities of olfactory 

 sensations, and they are more easily reduced to a few primary or 

 fundamental sensations. Sapid substances have generally been 

 divided into four classes as regards the fundamental sensations pro- 

 duced by them viz.: (i) Sweet, (2) acid, (3) bitter, (4) salinei 

 All taste sensations seem to be combinations of these, or combina- 

 tions of one or more of them with olfactory sensations, or with sensa- 

 tions due to excitation of the ordinary sensory nerves of the tongue. 



Sweet and acid tastes are best appreciated by the tip, and bitter 

 tastes by the base, of the tongue. Differences have been detected 

 between indiridual papillae in their power o-f reaction to sapid sub- 



