PHYSIOLOGY 117 



Reaction to light stimuli. Most Protozoa seem to be indifferent 

 to the ordinary light, but when the light intensity is suddenly in- 

 creased, there is usually a negative reaction. Verworn saw the di- 

 rection of movements of an amoeba reversed when its anterior end 

 was subjected to a sudden illumination; Rhumbler observed that an 

 amoeba, which was in the act of feeding, stopped feeding when it 

 was subjected to strong light. According to Mast, Amoeba pro- 

 tens ceases to move when suddenly strongly illuminated, but con- 

 tinues to move if the increase in intensity is gradual and if the il- 

 lumination remains constant, the amoeba begins to move. According 

 to Jennings, Stentor coeruleus reacts negatively against light. 



The positive reaction to light is most clearly shown in stigma- 

 bearing Mastigophora, as is well observable in a jar containing 

 Euglena, Phacus, etc., in which the organisms collect at the place 

 where the light is strongest. If the light is excluded completely, 

 the organisms become scattered throughout the container, inac- 

 tive and sometimes encyst, although the mixotrophic forms would 

 continue activities by saprozoic method. The positive reaction to 

 light by chromatophore-bearing forms enables them to find places 

 in the water where photosynthesis can be carried on to the maximum 

 degree. 



All Protozoa seem to be more sensitive to ultraviolet rays. Inman 

 found that amoeba shows a greater reaction to the rays than others 

 and Hertel observed that Paramecium which was indifferent to an 

 ordinary light, showed an immediate response (negative reaction) to 

 the rays. MacDougall brought about mutations in Chilodonella by 

 means of these rays (p. 181). When ciliates are vitally stained with 

 eosin, erythrosin, etc., they react sometimes positively or negatively 

 as in Paramecium (Metzner), or always negatively, as in Spiro- 

 stomum(Blattner). According toEfimoff, 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, however, long exposure to the rays was 

 fatal to Protozoa, the first ejffect of exposure being shown by accele- 

 rated movement. Halberstaedter 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, 



