GUSTATORY SENSATIONS. 



825 



Taste-bulbs. The end-organs of the gustatory nerves are the taste-bulbs or taste-buds dis- 

 covered by Schwalbe and Loven (1867). They occur on the lateral surfaces of the circumvallate 

 papillae (fig. 606, I), and upon the opposite side, K, of the fossa or capillary slit, R, R, which 

 surrounds the central eminence or papilla ; they occur more rarely on the surface. They also 

 occur on the fungiform papillae, in the papillae of the soft palate and uvula (A. Hoffmann), on 

 the under surface of the epiglottis, the upper part of the posterior surface of the epiglottis, and 

 the inner side of the arytenoid cartilages ( Verson, Davis), and on the vocal cords (Simanowsky). 

 Many buds or bulbs disappear in old age. 



[In the rabbit and some other animals, there is a folded laminated organ on each side of the 

 posterior part of the tongue, called the papilla foliata ; the folds have on each side of them 

 numerous taste-buds (fig. 607).] 



Structure of the taste-bulbs. They are 81 jx high and 33 /* thick, barrel-shaped, and embedded 

 in the thick stratified squamous epithelium of the tongue. Each bulb consists of a series of 

 lancet-shaped, bent, nucleated, outer supporting or protective ceUs, arranged like the staves 

 of a barrel (fig. 606, II, D, insolated in III, a). They are so arranged as to leave a small 

 opening, or the "gustatory pore," at the free end of the bulb. Surrounded by these cells, 

 and lying in the axis of the bud, are 1 to 10 gustatory cells (II, E), some of which are provided 

 with a delicate process (III, e) at their free ends, while their lower fixed ends send out basal 

 processes, which become continuous with 

 the terminations of the nerves of taste, 

 which have become non-medullated. 

 After section of the glossopharyngeal, 

 the taste-buds degenerate, while the 

 protective cells become changed into 

 ordinary epithelial cells within four 

 months (v. Vintschgau and Hbnig- 

 schmied). Very similar structures were 

 found by Ley dig in the skin of fresh- 

 water fishes. The glands of, the tongue 

 and their secretory fibres from the 9th 

 cranial nerve are referred to in 141 

 (Drasch). 



423. GUSTATORY SENSA- 

 TIONS. Varieties. There are 

 four different gustatory qualities, 

 the sensations of 1. Sweet; 2. 

 Bitter ; 3. Acid ; 4. Saline. Acid 

 and saline substances at the same 

 time also stimulate the sensory 

 nerves of the tongue, but when 



Epithelium. 



Fig. 607. 



greatly diluted, they only excite the Vertical section of two septa of the papilla foliata 

 end-organs of the specific nerves of (rabbit), x 80. Each septum, I, has secondary septa, 

 taste. Perhaps there are special *{> taste-buds ; medullated nerve; ^serous 

 .,, r i TiT . r gland, and part of its duct, a : M, muscular fibres oi 



nerve-fibres for each different gusta- he tongue. 

 tory quality (u. Vintschgau). 



Conditions. Sapid substances, in order that they may be tasted, require the 

 following conditions : They must be dissolved in the fluid of the mouth, especially 

 substances that are solid or gaseous. The intensity of the gustatory sensation 

 depends on : 1. The size of the surface acted on. Sensation is favoured by rub- 

 bing in the substance between the papillae, in fact, this is illustrated in the rubbing 

 movements of the tongue during mastication ( 354). 2. The concentration of the 

 sapid substance is of great importance. Valentin found that the following series 

 of substances ceased to be tasted in the order here stated, as they were gradually 

 diluted syrup, sugar, common salt, aloes, quinine, sulphuric acid. Quinine cau 

 be diluted 20 times more than common salt and still be tasted (Camerer). 3. The 

 time which elapses between the application of the sapid substance and the produc- 

 tion of the sensation varies with different substances. Saline substances -are tasted 

 most rapidly (after 0*17 second, according to v. Vintschgau), then sweet, acid and 

 bitter (quinine after 0*258 second, v. Vintschgau). This even occurs with a 

 mixture of these substances (Schirmer). The last-named substances produce the most 



