THE SENSE- OF TASTE. 851 



sense of smell by coming into contact with the olfactory epithelium after solu- 

 tion in the layer of moisture covering it. This epithelium is easily thrown 

 out of function, as the common loss of smell when there is a " cold in the 

 head " testifies. When the nostril is filled with water in which an odorous 

 substance is dissolved, no sensation of smell is excited, but it is said that if 

 normal salt-solution, which injures the living tissues less than water, be used 

 as the solvent, the odor can still be perceived. In many lower animals the 

 sense of smell has an acuteness and an importance in their economy unknown 

 in the human race. It is probable that not only do different races have their 

 distinctive odors, but that each individual exhales an odor peculiar to himself, 

 distinguishable by the olfactory organs of certain animals. The classification 

 of odors is not very definite, and the relation of odors to one another in the 

 way of contrast and harmony is ill understood. No limited number of pri- 

 mary sensations, as in vision, have been discovered out of which other sen- 

 sations can be composed. Certain sensations, as those due to the inhalation 

 of ammonia and other irritant gases, are thought to be due to excitement of 

 the nasal filaments of the fifth nerve, and not of the olfactory. 



Subjective sensations of smell are sometimes experienced, the result of some 

 irritation arising in the olfactory apparatus itself. 



Finally, in man sensations of smell have their most important uses in con- 

 nection with taste ; many so-called " tastes " owe their character wholly or 

 partly to the unconscious excitement of the sense of smell. 



G. TASTE. 



The peripheral surfaces concerned in taste include, in variable degree, the 

 upper surface and sides of the tongue and the anterior surfaces of the soft 

 palate and of the anterior pillars of the fauces. Other parts of the buccal 

 and pharyngeal cavities are, in most persons, devoid of taste. 1 



The chief peripheral sensory organs of taste are groups of modified epi- 

 thelial cells, known as taste-buds (Fig. 293), seated in certain papillae of the 

 tasting surfaces. According to some authors, only parts provided with taste- 

 buds can give taste-sensations. 2 



The structure of taste-buds is most easily studied in the papilla foliata of 

 the rabbit, a patch of fine, parallel wrinkles found on each side of the 

 back part of the tongue of the animal. The taste-bud is a somewhat globular 

 body seated in the folds of mucous membrane between the furrows of the 

 papilla. It is made up of a sheath of flattened, fusiform cells enclosing a 

 number of rod-like cells each of which terminates in a hair-like process. These 

 cells surround a central pore which opens into a furrow of the papilla. 

 The hair-bearing cells recall the appearance of the olfactory rod-cells, and 

 are probably the true sensory cells of taste, since between them terminate the 

 filaments of the gustatory nerve. In the human tongue taste-buds are con- 



1 V. Vintschgau : " Geruchsinn," Hermann's Handbuch der Physiologie, iii. 2, 1880. 



2 Camerer: Zeitschrift fur Biologic, 1870, vi. S. 440; Wilczynsky : Hofmann und Schwalbe's 

 Jahresbericht der Physiol., 1875. 



