PHYSIOLOGY 113 



man found that amoebae show a greater reaction to the rays and 

 Hertel observed that Paramecium which were indifferent to an 

 ordinary hght, showed an immediate response (negative reac- 

 tion) to the rays. MacDougall brought about mutations in Chilo- 

 donella by means of these rays (p. 164). When ciUates are vitally 

 stained with eosin, erythrosin, etc., they react sometimes posi- 

 tively or negatively, as in Paramecium (Metzner), or always neg- 

 atively, as in Spirostomum (Blattner). According to Efimoff, this 

 "induced phototaxis" is not limited to fluorescent dyes, but also 

 is possessed by all vital-staining dyes. Zuelzer (1905) studied the 

 effects of radium rays upon various Protozoa and found that the 

 effect was not the same among different species. For example, 

 limax amoeba was more resistant than others. In all cases, how- 

 ever, long exposure to the rays was fatal to Protozoa, the first ef- 

 fect of exposure being shown by accelerated movement. Halber- 

 staedter and Luntz (1929) studied injuries and death of Eudorina 

 elegans by exposure to radium rays. Joseph and Prowazek (1902) 

 found Paramecium and Volvox gave negative response to the 

 rontgen-ray. 



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 repro- 

 duction. 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 environ- 

 ment. In the case of parasitic Protozoa which pass their life-cycle 

 in warm-blooded and cold-blooded host animals, such as Plasmo- 

 dium and mammalian trypanosomes, the change in body tem- 

 perature 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 

 reaction to the anode and moves toward the cathode either by 

 reversing 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 



