88 THE BEHAVIOR OF PROTOZOA 



sistency which the animals might undergo would so greatly 

 influence the result. The fact described by Day and Bentley 

 that Paramcecia which had acquired a facility of turning 

 still showed the effects of their experience after having been 

 placed for an interval of twenty minutes in their culture 

 medium may well be due to the persistence of the purely 

 physiological or pathological effects of their previous con- 

 finement. 



Smith devised another experiment to show the modifica- 

 tion of the reaction of Paramcecium to changes of temperature. 

 A tube containing several Paramoecia was so arranged that 

 either end could be heated or cooled at will. When one end 

 was heated the Paramoecia would dart about at random, and 

 when they swam into the cooler water they would often turn 

 back to the hot water again. After the temperature of the 

 two ends of the tube was reversed the animals would dart 

 about much as before, reaching the cool water only after a 

 number of trials. With repeated reversals, however, the 

 movements of the Paramo3cia became "slower and more 

 regulated" and they would "seldom turn more than once 

 toward the cold water before swimming in that direction." 

 According to Smith, Paramcecium does not give evidence of 

 the possession of associative memory, but he concludes that 

 "its behavior may be modified to show the results of practice, 

 both in a reduction of the time involved in performing a 

 movement and in the increase of the suitability of the move- 

 ment to accomplish the appropriate result." The modified 

 reaction to temperature, I believe, may be accounted for not 

 so much through the effect of practice in the performance 

 of an act, but as a consequence of a general diminution of 

 excitability. Take a few drops of a Paramoecium culture 

 and place them on a slide. For a time the animals scurry 

 about in the greatest haste and confusion, and frequently 



