PHYSIOLOGY 135 



(1948) noted: dosages higher than 100,0Q0r retard the locomotion of 

 the ciliate; none survives 700,000r; the symbiotic Chlorella is de- 

 stroyed by exposure to 300,000-000,000?' ; irradiation inhibits di- 

 division temporarily, but the animals recover normal division rate 

 after certain length of time; and mating types are not destroyed, 

 though minor changes occur. In Pelomyxa carolinensis, Daniels 

 (1951) observed: the median lethal dose of X-rays is 96,000r; with 

 dosages 15,000-140,000r, the first plasmotomy is greatly delayed and 

 the second plasmotomy is also somewhat delayed, but later plas- 

 motomies show complete recovery; X-irradiation does not change 

 the type of plasmotomy; and in individuals formed by plasmogamy 

 of X-irradiated halves to non-irradiated halves, the nuclei divide 

 simultaneously as in a normal individual. 



Reaction to temperature stimuli. As was stated before, there 

 seems to be an optimum temperature range for each protozoan, 

 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 inhabit two hosts: warm-blooded and cold- 

 blooded animals, such as Plasmodium and Leishmania, the difference 

 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. When Paramecium caudatum was exposed to a high- 

 frequency electrostatic or electromagnetic field, Kahler, Chalkley 

 and Voegtlin (1929) found the effect was primarily caused by a tem- 

 perature increase in the organism. By subjecting Pelomyxa carolin- 

 ensis to a direct current electric field, Daniel and May (1950) noted 

 that the time required for the rupture of the body in a given current 



