THE SENSE OF TASTE. 



853 



The sensitiveness of taste-sensation is greatest when the exciting substance 

 is at the temperature of the body. Weber l found that when the tongue was 

 dipped during one-half to one minute in water either at the freezing tempera- 

 ture or warmed to 50 C., the sweet taste of sugar could no longer be appre- 

 ciated by it. It is probable that sapid substances reach the sensory endings 

 of the nerves of taste only after being dissolved in the natural fluids of the 

 mouth, and any artificial drying of the buccal surfaces or alteration of their 

 secretion must affect taste-perceptions. 



The excitement of the taste-nerves appears to depend not so much on the 

 absolute amount of the substance to be detected as on the concentration of the 



Auditory. 



Gustatory. 



Tactile. 



FIG. 294. Diagram showing the mode of termination of sensory nerve-fibres in the auditory, gustatory, 

 and tactile structures of vertebrata (from Quain, after Retzius). Each sense organ may be considered as 

 essentially constructed of a nerve-cell with two processes, one finding its way centrally to cluster round 

 other nerve-cells or their processes, and the other to terminate in the periphery. In the organ of smell 

 the peripheral process is very short and is directly irritated by foreign particles, the original nerve-cell 

 being represented by the olfactory cell (Fig. 291). In the organs of touch the nerve-cell is found in the 

 ganglion of the posterior spinal nerve-root ; the peripheral process is very long and is acted on indirectly 

 through the modified epithelium round which it clusters. The same may be said of the other sense 

 organs. See Quain's Anatomy, 10th ed., vol. iii. pt. 3, p. 152. 



solution containing it. Thus, when 1 part of common salt to 213 of water 

 was tasted by Valentin, 2 11 cubic centimeters of the fluid was sufficient to give 

 a saltish taste ; when diluted so that the ratio of salt to water was 1 to 426, 

 12 cubic centimeters taken in the mouth scarcely gave the salt taste. Sulphate 

 of quinine dissolved in the proportion 1 to 33,000 gave a decided bitter taste, 

 but a solution 1 to 1,000,000 was with difficulty perceived as bitter. 



It has generally been conceded that all gustatory sensations may be built 

 up out of four primary taste-sensations namely, bitter, sweet, sour, and salt. 

 Some authors even limit the list to tastes of bitter and sweet (V. Vintschgau), 



1 Archivfiir Anatomic und Physiologic, 1847, S. 342. J Lehrbuch der Physiologic, 1848. 



