312 THE INTERNAL ENVIRONMENT OF THE BODY Part III 



character. Taste and smell are closely allied to the common chemical sense 

 from which they sprang. The catfish, Amiurus, has taste buds along the sides 

 of its body and will turn and snap at bait that is suspended near its flank. Its 

 skin can be stimulated by very weak chemical solutions even after its taste 

 buds have been isolated by cutting the nerves leading to them. 



Taste. The sensation of taste never acts separately as vision and hearing 

 do. Smell plays the largest part in what is called taste, and pressure and 

 temperature have their shares in it. By one or another kind of receptor we 

 not only perceive the sourness of lemonade, but its temperature, its weight 

 on the tongue, and the consistency which helps or hinders its spread over the 

 tongue. Substances can be tasted only when they are in solution and their 

 molecules are moving about freely. 



Fig. 17.2. Sense of smell in honeybees. Outline 

 of head showing segments of antennae. Cutting an 

 antenna at the line aa leaves one segment that bears 

 sense organs of smell. Cutting at bb leaves no sense 

 of smell. See also figure 30.27. 



Taste and smell are highly developed in insects and because of this, insects 

 are important to humanity both for good and bad. Bees smell and taste nectar 

 and pollen, and in gathering them accomplish the cross-pollination on which 

 the production of many fruits depends (Fig. 17.2). Their sense of smell 

 guides certain moths and butterflies to lay their eggs on particular host plants 

 on which the young caterpillars will feed. But the same moths and butterflies 

 will readily lay eggs on the wrong kinds of plants if they have been sprayed 

 with extracts of the host plants. Houseflies are quickly attracted by odors of 

 food, fruitflies (Drosophila) by ripening fruit, and female mosquitoes by 

 body odors. Ants, bees, and wasps smell through their antennae, as is readily 

 shown by tests made after these have been removed. Honeybees can taste 

 by receptors in their mouth parts and they as well as the wasps, Vespa and 

 Polistes, can distinguish plain from sweetened water. They also can recog- 

 nize sweet, bitter, and salt as separate qualities. Out of 34 sugars and related 

 substances, 30 are sweet to human taste, but only nine are sweet to honeybees 

 and all of these are in their natural foods. The sweeter the mixture of cane 

 sugar, the more of it the worker honeybees will drink. The sweeter the 

 mixture that foraging honeybees discover, the more will they excite workers 

 in the home hive by dancing when they return from successful foraging trips. 



