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TOUCH— FIELDWORK AND EXPERIMENTS 



Just as there are close affinities between the senses of smell 

 and taste, there are similar affinities in respect of touch and 

 hearing. Sound waves can be felt as well as heard, and in 

 observing animals in order to find out whether, and to what 

 extent, they respond to touch, this must be taken into con- 

 sideration. For instance, fishes and snakes cannot "hear" in 

 the normal way in which we use that word, but both are 

 most responsive to vibrations in water or on land, and in 

 carrying out any experiments aimed at demonstrating the 

 sense of touch (or feeling), care must be taken not to draw 

 conclusions which are not accurate. 



Many of the lower organisms — even unicellular ones — are 

 sensitive to touch; and this can be shown by arranging 

 under a microscope a slide on which a drop of water has 

 been placed containing a colony of the organism vorticella, 

 which has been referred to in a previous chapter. It will be 

 remembered that vorticellae respond to a tap on the slide 

 containing some of these primitive animals and, as stated 

 before, the vibrations set in motion will cause the organisms 

 to retract their stalks. Now, if it is desired to produce evidence 

 of response to a direct touch, it will be necessary to set up 

 your colony in a "trough" rather than on a simple slide. It 

 will also be necessary to have at hand either a very fine 

 piece of platinum wire, or the finest of bristles with which 

 you can provide yourself. Then you must wait until the 

 vorticellae are in a state of maximum stretch and leave them 

 undisturbed for a few seconds while you pick up your wire 

 or bristle. Moving with the greatest care, gently insert the 

 wire into the trough and very slowly move the wire until it is 

 brought into direct contact with one of the vorticella. As 

 soon as this happens, the individual touched will retract 

 and this reaction will be communicated to others in the 



colony which will do likewise. 



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