THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



sz 



the Paramecium turns in the same manner as before, — toward the 

 aboral side, and hence toward the point touched. This experiment is 

 more easily performed, and the results are more striking, with certain 

 of the Hypotricha,' because these animals do not continually revolve on 

 the long axis, as Paramecium does. 



The general effect of the avoiding reaction is to cause the animals 

 to avoid and escape from the region in which the stimulus is acting. 

 This may be illustrated for the different classes of stimuh in the follow- 

 ing ways. 



The effects of this reaction to chemicals may best be seen by intro- 

 ducing a httle ^ per cent solution of sodium chloride into the water 

 containing the ani- 

 mals. For this pur- 

 pose water with many 

 Paramecia is placed 

 on a slide and covered 

 with a long cover- 

 glass supported near 

 its end by glass rods. 

 A medicine dropper 

 is drawn to a long, 

 slender point, and with 

 this a drop of the salt 

 solution is introduced 

 beneath the cover-glass, as illustrated in Fig. 40. The Paramecia are 

 swimming about in all directions, but as soon as they come to the 



region of the salt solution, the 

 avoiding reaction is given in the 

 way already described, and 

 the animals swim elsewhere. 

 Thus the drop of salt solution 

 remains empty (Fig. 41). 



Practically all strong chemicals 

 induce the avoiding reaction, so 

 that Paramecia do not enter them. 

 This has been shown for many 

 alkahes, neutral salts, and organic substances, and for strong acids. 

 In the case of acids the reaction differs in certain respects from the 

 behavior under the influence of other chemicals ; this will be brought 



out later. 



The reaction to heat or cold may easily be shown by placing a drop 



iSee Chapter VII. 



Fig. 40. — Method of introducing 

 of infusoria. 



chemical into a slide 



Fig. 41. — Slide of Paramecia four minutes 

 after the introduction of a drop of J per cent 

 NaCl. The drop remains empty. 



