Smith, Educahihty of Paramceciiun. 



507 



As this facing about in the tube is repeated, the time taken for 

 each turn may be longer than for the last, the animal finally dying 

 of apparent fatigue, or, if the tube is not so small that too violent 

 an effort is required of the animal, the time may gradually be 

 shortened and a most surprising aptitude of turning be developed. 

 Paramoecia from a vigorous culture give better results than poorly 

 nourished ones. Under optimum conditions I have found a reduc- 

 tion of turning time, after the animals have been in the tube for 

 twelve hours or more, from four or five minutes to a second or two, 

 which is the minimum time in which the turn can be made. 



Often the Paramoecium will rest for a long period at one menis- 

 cus, slowly circling around with its buccal groove resting against 

 the air surface. When, however, the effort is made to reverse, the 

 shortening of time in the practiced individuals is very apparent. 



Fig. 2. A and A', tubes through which water of alternating temperatures passes and on which the 

 capillary tube rests. £, beaker of boiling water in which pipe coil is immersed. C and C, cold water 

 supply tubes. H, hot water supply tube. and 0', interrupters. S, switch which alternates tem- 

 peratures in A and A'. T, capillary tube containing Paramoecium. 



At and 0' are two interrupters so arranged that a single lever raises one and lowers the other. If 

 the interrupter at presses on the pipes the water flows through the loops, the hot water (from H) flow- 

 ing through A' and the cold water (from C) flowing through A. If the interrupter at 0' presses upon 

 the pipes the hot water flows through A and the cold water through A'. The temperature and flow of 

 the water supply are kept constant so that the alternating temperatures at A and A' do not vary. 



Reactions to temperature. In these experiments a capillary tube 

 was selected large enough to allow the Paramoecia to reverse their 

 direction without touching its sides, and in which two Paramoecia 

 could pass each other without difficulty. A number of individuals 

 were taken up in this tube and the tube was placed on a carriage 

 having two large glass supporting tubes through which water 

 of different temperatures was passing and on which the capillary 

 tube rested (fig. 2). 



While hot water was flowing through one support and cold 

 water through the other the temperatures could be reversed, by a 



