ECOLOGY 25 



morphological changes in the experimental protozoans which might 

 be attributed to the presence of the salt in the water, except Amoeba 

 verrucosa, in which certain structural and physiological changes were 

 observed as follows: as the salinity increased, the pulsation of the 

 contractile vacuole became slower. The body activity continued up 

 to 44 per cent sea water and the vacuole pulsated only once in 40 

 minutes, and after systole, it did not reappear for 10-15 minutes. 

 The organism became less active above this concentration and in 

 84 per cent sea water the vacuole disappeared, but there was still a 

 tendency to form the characteristic ridges, even in 91 per cent sea 

 water, in which the organism was less fan-shaped and the cytoplasm 

 seemed to be more viscous. Yocom (1934) found that Ewplotes pa- 

 tella was able to live normally and multiply up to 66 per cent of 

 sea water; above that concentration no division was noticed, though 

 the organism lived for a few days in up to 100 per cent salt water, 

 and Paramecium caudatum and Spirostomum ambiguum were less 

 adaptive to salt water, rarely living in 60 per cent sea water. Frisch 

 (1939) found that no freshwater Protozoa lived above 40 per cent 

 sea water and that Paramecium caudatum and P. multimicronucle- 

 atum died in 33-52 per cent sea water. Hardin (1942) reports that 

 Oikomonas termo will grow when transferred directly to a glycerol- 

 peptone culture medium, in up to 45 per cent sea water, and cultures 

 contaminated with bacteria and growing in a dilute glycerol-peptone 

 medium will grow in 100 per cent sea water. 



Hydrogen-ion concentration. Closely related to the chemical com- 

 position is the hydrogen-ion concentration (pH) of the water. Some 

 Protozoa appear to tolerate a wide range of pH. The interesting pro- 

 teomyxan, Leptomyxa reticulata, occurs in soil ranging in pH 4.3 to 

 7.8, and grows very well in non-nutrient agar between pH 4.2 and 

 8.7, provided a suitable bacterial strain is supplied as food (Singh, 

 1948) ; and according to Loefer and Guido (1950), a strain of Euglena 

 gracilis (var. bacillaris) grows between pH 3.2 and 8.3. However, the 

 majority of Protozoa seem to prefer a certain range of pH for the 

 maximum metabolic activity. 



The hydrogen-ion concentration of freshwater bodies varies a great 

 deal between highly acid bog waters in which various testaceans 

 may frequently be present, to highly alkaline water in which such 

 forms as Acanthocystis, Hyalobryon, etc., occur. In standing deep 

 fresh water, the bottom region is often acid because of the decom- 

 posing organic matter, while the surface water is less acid or slightly 

 alkaline due to the photosynthesis of green plants which utilize car- 

 bon dioxide. In some cases different pH may bring about morpho- 



