PHYSIOLOGY 



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the organism avoided the obstacle by reversing a part of the current 

 and flowing in another direction (c) . When an amoeba is stimulated 

 mechanically by the tip of a glass rod (rf), it turns away from the 

 side touched, by changing endoplasmic streaming and forming new 

 pseudopodia (e). Positive reactions are also often noted, when a 

 suspended amoeba (/) comes in contact with a solid surface with the 

 tip of a pseudopodium, the latter adheres to it by spreading out (g). 

 Streaming of the cytoplasm follows and it becomes a creeping form 



Fig. 50. Reactions of amoebae to mechanical stimuli (Jennings), a-c, 

 an amoeba avoiding an obstacle; d, e, negative reaction to mechanical 

 stimulation; f-h, positive reaction of a floating amoeba. 



(h). Positive reactions toward solid bodies account of course for the 

 ingestion of food particles. 



In Paramecium, according to Jennings, the anterior end is more 

 sensitive than any other parts, and while swimming, if it comes in 

 contact with a solid object, the response may be either negative or 

 positive. In the former case, avoiding movement (Fig. 51, c) follows 

 and in the latter case, the organism rests with its anterior end 

 or the whole side in direct contact with the object, in which position 

 it ingests food particles through the cytostome. 



Reaction to gravity. The reaction to gravity varies among dif- 

 ferent Protozoa, according to body organization, locomotor organ- 

 elle, etc. Amoebae, Testacea and others which are usually found 

 attached to the bottom of the container, react as a rule positively 



