THE SPECIAL SENSES 3Y5 



of both points will give the sensation of but a single con- 

 tact. Eepeat the experiment on the tip of the forefinger, 

 and both points will be felt until the points are only about 

 one tenth of an inch apart. 



293. The sense of taste. The sense of taste enables us to 

 test in some degree the chemical constitution of substances 

 which are taken into the mouth as food. We discriminate 

 by the taste organs between good food and bad, well-tasting 

 and ill-tasting. These organs are, with us and the other air- 

 breathing animals, located in the mouth or on the mouth 

 parts. They must be located so as to come into contact 

 with the food, and it is also necessary that the food sub- 

 stance to be tasted be made liquid. This is accomplished 

 by the fluids poured into the mouth from the salivary 

 glands. With the lower aquatic animals it is not improb- 

 able that taste organs are situated on other parts of the 

 body besides the mouth, and that taste is used not only to 

 test food substances, but also to test the chemical char- 

 acter of the fluid medium in which they live. 



The taste organs are much like the tactile organs, ex- 

 cept that the special taste cell is exposed, so that small par- 

 ticles of the substance to be tasted can come into actual 

 contact with it. The nerve-ending is usually in a small 

 raised papilla or depressed pit. In the simplest animals 

 there is no special organ of taste, and yet Amoeba and 

 other Protozoa show that they appreciate the chemical con- 

 stitution of the liquid in which they lie. They taste that 

 is, test the chemical constitution of the substances by 

 means of their undifferentiated body surface. The taste 

 organs are not always to be told from the organs of smell. 

 Where an animal has a certain special seat of smell, like 

 the nose of the higher animals, then the special sense 

 organs of the mouth can be fairly assumed to be taste 

 organs ; but where the seat of both smell and taste is in 

 the mouth or mouth parts, it is often impossible to distin- 

 guish between the two kinds of organs. 



