132 



PROTOZOOLOGY 



toward gravity, while others manifest negative reaction as in the 

 case of Paramecium (Jensen; Jennings), which explains in part why 

 Paramecium in a culture jar are found just below the surface film in 

 mass, although the vertical movement of P. caudatum is undoubt- 

 edly influenced by various factors (Koehler, 1922, 1930; Dembowski, 

 1923, 1929, 1929a; Merton, 1935). 



Reaction to current. Free-swimming Protozoa appear to move 

 or orientate themselves against the current of water. In the case of 



Fig. 51. Reactions of Paramecium (Jennings), a, collecting in a drop 

 of 0.02% acetic acid; b, ring-formation around a drop of a stronger solu- 

 tion of the acid; c, avoiding reaction. 



Paramecium, Jennings observed the majority place themselves in 

 line with the current, with anterior end upstream. The mycetozoan 

 is said to exhibit also a well-marked positive reaction. 



Reaction to chemical stimuli. When methylgreen, methylene 

 blue, or sodium chloride is brought in contact with an advancing 

 amoeba, the latter organism reacts negatively (Jennings). Jen- 

 nings further observed various reactions of Paramecium against 

 chemical stimulation. This ciliate shows positive reaction to weak 

 solutions of many acids and negative reactions above certain con- 

 centrations. For example, Paramecium enters and stays within the 



