ECOLOGY 21 



and 7.6, excess of potassium decreases resistance and excess of cal- 

 cium increases resistance. Glaser and Coria (1933) cultivated Para- 

 mecium caudatum on dead yeast free from living organisms at 

 20-28°C. (optimum 25°C.) and noted that at 30°C. the organisms 

 were killed. Doudoroff (1936), on the other hand, found that in 

 P. multimicronucleatum its resistance to raised temperature was low 

 in the presence of food, but rose to a maximum when the food was 

 exhausted, and there was no appreciable difference in the resistance 

 between single and conjugating individuals. 



The thermal waters of hot springs have been known to contain liv- 

 ing organisms including Protozoa. Glaser and Coria' (1935) obtained 

 from the thermal springs, of Virginia, several species of Mastigoph- 

 ora, Ciliata, and an amoeba which were living in the water, the tem- 

 perature of which was 34-36°C, but did not notice any protozoan in 

 the water which showed 39-41°C. Uyemura (1936, 1937) made a 

 series of studies on Protozoa living in various thermal waters of Ja- 

 pan, and reported that many species lived at unexpectedly high 

 temperatures. Some of the Protozoa observed and the temperatures 

 of the water in which they were found are as follows: Amoeba sp., 

 Vahlkampfia Umax, A. radiosa, 30-51°C; Amoeba verrucosa, Chilo- 

 donella sp., Lionotus fasciola, Paramecium caudatum, 36-40°C; 

 Oxytricha fallax, 30-56°C. 



Under experimental conditions, it has been shown repeatedly that 

 many protozoans become accustomed to a very high temperature if 

 the change be made gradually. Dallinger (1887) showed a long time 

 ago that Tetramitus rostratus and two other species of flagellates 

 became gradually acclimatized up to 70°C. in several years. In na- 

 ture, however, the thermal death point of most of the free-living 

 Protozoa appears to lie between 36° and 40°C. and the optimum 

 temperature, between 16° and 25°C. 



On the other hand, the low temperature seems to be less detri- 

 mental to Protozoa than the higher one. Many protozoans have 

 been found to live in water under ice, and several haematochrome- 

 bearing Phytomastigina undergo vigorous multiplication on snow in 

 high altitudes, producing the so-called "red snow." Klebs (1893) sub- 

 jected the trophozoites of Euglena to repeated freezing without ap- 

 parent injury and Jahn (1933) found no harmful effect when Euglena 

 cultures were kept without freezing at — 0.2°C. for one hour, but 

 when kept at — 4°C. for one hour the majority were killed. Gay lord 

 (1908) exposed Trypanosoma gambiense to liquid air for 20 minutes 

 without apparent injury, but the organisms were killed after 40 min- 

 utes' immersion, 



