118 PROTOZOOLOGY 



although it can withstand temperatures which are lower or higher 

 than that range. As a general rule, the higher the temperature, the 

 greater the metabolic activities, and the latter condition results in 

 turn in a more rapid growth and more frequent reproduction. It has 

 been suggested that change to different phases in the life-cycle of a 

 protozoan in association with the seasonal change may be largely 

 due to temperature changes of the environment. In the case of 

 parasitic Protozoa which pass their life-cycle in two hosts: warm- 

 blooded and cold-blooded animals, such as Plasmodium and mam- 

 malian trypanosomes, the change in body temperature of host 

 animals may bring about specific stages in their development. 



Reaction to electrical stimuli. Since Verworn's experiments, 

 several investigators studied the effects of electric current which 

 is passed through Protozoa in water. Amoeba shows negative re- 

 action to the anode and moves toward the cathode either by revers- 

 ing the cytoplasmic streaming (Verworn) or by turning around the 

 body (Jennings). The free-swimming ciliates move mostly toward 

 the cathode, but a few may take a transverse position (Spirostomum) 

 or swim to the anode (Paramecium, Stentor, etc.). Of flagellates, 

 Verworn noticed that Trachelomonas and Peridinium moved to the 

 cathode, while Chilomonas, Cryptomonas, and Polytomella, swam 

 to the anode. 



References 

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, S. R. Hall, E. P. Sanders and J. Collier 1934 The 



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