50 



CILIATE PROTOZOA 



mg. of Congo Red is boiled for ten minutes with a few ml. of 

 water and then fed to the ciHates. The indicator turns blue at 

 pH 3. The animal is able to some extent to distinguish between 

 particles which are good for food, and those such as carmine 

 which are inert. Moreover, having been deceived experimentally 

 by carmine it learns to avoid it in the future, and can remember 

 to do so for two or three days. 



EFFECT OF STIMULI 



Like all other organisms, Paramecitim shows automatism. Its 

 incessant activity is spontaneous, but is continually modified 



a 



, - ' 



> » ' 



10'- 



25- 



FiG. 25. — The reaction of Paramecia to heat 



and cold. — From Jennings, after 



Mendelssohn. 



At a., the Paramecia are placed in a trough both ends of 

 which have a temperature of 19° C. They are equally 

 scattered. At b, the temperature of one end of the 

 trough is raised to 38° C, while the other is only 26° C. 

 The Paramecia collect at the end which has the lower 

 temperature. At c. one end has a temperature of 25° C. 

 while the other i ; lowered to 10° C. The animalcules 

 now collect at the end which has the higher 

 temperature. 



Fig. 26. — Paramecia collecting in a drop of 0-02 

 per cent, acetic acid. — From Jennings 



