ECOLOGY 19 



Kiihn (1864) observed that Amoeba and Actinophrys suffered no 

 ill effects when kept at 0°C. for several hours as long as the culture 

 medium did not freeze, but were killed when the latter froze. Molisch 

 (1897) likewise noticed that Amoeba dies as soon as the ice forms in 

 its interior or immediate vicinity. Chambers and Hale (1932) dem- 

 onstrated that internal freezing could be induced in an amoeba by 

 inserting an ice-tipped pipette at — 0.6°C., the ice spreading in the 

 form of fine featherly crystals from the point touched by the pipette. 

 They found that the internal freezing kills the amoebae, although 

 if the ice is prevented from forming, a temperature as low as — 5°C. 

 brings about no visible damage to the organism. At 0°C., Deschiens 

 (1934) found the trophozoites of Entamoeba histolytica remained 

 alive, though immobile, for 56 hours, but were destroyed in a short 

 time when the medium froze at — 5°C. 



According to Greeley, when Stentor coeruleus was slowly sub- 

 jected to low temperatures, the cilia kept on beating at 0°C. for 1-3 

 hours, then cilia and gullet were absorbed, the ectoplasm was thrown 

 off, and the body became spherical. When the temperature was 

 raised, this spherical body is said to have undergone a reverse proc- 

 ess and resumed its normal activity. If the lowering of temperature 

 is rapid and the medium becomes solidly frozen, Stentor perishes. 

 Efimoff (1924) observed that Paramecium multiplied once in about 

 13 days at 0°C., withstood freezing at — 1°C. for 30 minutes, but died 

 when kept for 50-60 minutes at the same temperature. He further 

 stated that Paramecium caudatum, Colpidium colpoda, and Spiro- 

 stomum amhiguum, perished in less than 30 minutes, when ex- 

 posed below — 4°C., and that quick and short cooling (not lower than 

 — 9°C.) produced no injury, but if it is prolonged, Paramecium be- 

 came spherical and swollen to- 4-5 times normal size, while Colpid- 

 ium and Spirostomum shrunk. Wolfson (1935) studied Paramecium 

 sp. in gradually descending subzero-temperature, and observed that 

 as the temperature decreases the organism often swims backward, 

 its bodily movements cease at — 14.2°C., but the cilia continue to 

 beat for some time. While Paramecium recover completely from a 

 momentary exposure to — 16°C., long cooling at this temperature 

 brings about degeneration. When the water in which the organisms 

 are kept freezes, no survival was noted. Plasmodium knowlesi and 

 P. inui in the blood of Macacus rhesus remain viable, according to 

 Coggeshall (1939), for as long as 70 days at — 76°C., if frozen and 

 thawed rapidly. 



Light. In the Phytomastigina which include chromatophore-bear- 

 ing flagellates, the sun light is essential to photosynthesis (p. 92). The 



