360 THE SENSES 



The cerebral center of the gustatory nerve-fibers, it is likely, will be 

 shown to be low down on the mesial surface of the cortex of the temporal 

 lobe, just below one of the probable centers of smell. Von Bechterew 

 thinks he has located the center for bitter and salt in the anterior Sylvian 

 gyrus and for sour and sweet in the anterior ectosylvian gyrus (in apes), 

 in the region of the operculum. 



Some Characteristics of Taste. A substance in order to have a taste 

 must be at Jeast slightly soluble in the alkaline fluid of the mouth. Thus, 

 while iron gives a taste, sulphur does not. But not all substances solu- 

 ble in the mouth's secretions have tastes, and what it is that determines 

 whether or not a substance is to have a taste is quite unknown. There 

 is evidence that the taste-cells can be mechanically and electrically 

 stimulated to give gustatory sensations. This is an indication that 

 the taste of objects, like the "light" of the ether and the "sound " of 

 vibrating objects, is subjective, that is, resident in or the production of 

 the perceiving animal. Still sapid substances must have qualities of some 

 sort which determine their tastes. In this direction Haycraft finds 

 reasons to suppose that the compound chemical radicle COOH occasions 

 the acrid taste and CH 2 OH the sweet taste. 



No classification of the taste acceptable to all has yet been made. 

 In the nature of the sensations none is possible, perhaps. Some classifica- 

 tion may one day be made on the basis of the sensory cells. There is, 

 however, fairly good agreement that four classes of tastes are properly 

 described, namely sweet, bitter, salt, and sour. Seemingly a fifth taste, 

 metallic, should be added and perhaps a sixth, alkaline, although more 

 properly perhaps this is a variety of salt tastes. It is probable that all 

 the tastes are represented in every portion of the gustatory areas above 

 defined, but some parts give one taste more readily or more strongly 

 than another. Kiesow found the following threshold-values, the num- 

 bers being percentages of the substances in distilled water; about half a 

 cubic centimeter of the solution was used in each case. 



Perhaps one bud or even one taste-cell has to do with only one sort of 

 taste. Experimentation is difficult and more or less uncertain because 

 when the papillae are with difficulty made dry they are abnormal, but 

 when they are moist the liquid carries the sapid substances used as 

 stimuli to more than one end-organ. 



The reaction-time of the taste-buds differs with different substances: 

 salt is tasted most promptly and bitter least so. There are after-images 

 of taste as there are of vision and of the other senses. Various contrast- 



