ECOLOGY 17 



in saline with an excess of calcium, the acid maximum is the 

 higher; 3) in general acidity decreases and alkalinity increases re- 

 sistance; and 4) between pH 6.6 and 7.6, excess of potassium de- 

 creases resistance and excess of calcium increases resistance. 

 Glaser and Coria (1933) cultivated Paramecium 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. multimicronucleata 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 

 living organisms including Protozoa. Glaser and Coria obtained 

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

 phora, Ciliata, and an amoeba which were living in the water, the 

 temperature of which was 34-36°C., but did not notice any pro- 

 tozoan in the water which showed 39-4 1°C. Uyemura and his 

 co-workers made a series of studies on Protozoa living in various 

 thermal waters of Japan, and reported that many species lived 

 at unexpectedly high temperatures. Some of the Protozoa ob- 

 served 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, Chilodonella 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 tem- 

 perature if the change be made gradually. Dallinger and Drysdale 

 showed a long time ago that Tetramitus rostratus and two other 

 species of flagellates could be cultivated in temperatures ranging 

 from 16° to 70°C. In nature, 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 ones. 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." Efimoff 

 (1924) demonstrated that Paramecium, Frontonia, Colpidium 

 and other ciliates die quickly at — 4°C., but by a quick and short 



