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 Paramecia which had acquired a facility for 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 Parameecium to changes of temperature. 
A tube containing several Parameecia was so arranged that 
either end could be heated or cooled at will. When one end 
was heated the Paramecia 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 Paramcecia 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 Paramecium culture 
and place them on a slide. For a time the animals scurry 
about in the greatest haste and confusion, and frequently 
