22 PROTOZOOLOGY 



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 Eiiplotes 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 da3^s 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 

 (1935) 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 which 

 influences the distribution of Protozoa. The hydrogen-ion concentra- 

 tion of freshwater bodies vary 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, Hyalo- 

 bryon, etc., occur. In standing deep fresh water, the bottom region 

 is often acid because of the decomposing organic matter, while the 

 surface water is less acid or slightly alkaline due to the photosyn- 

 thesis of green plants which utilize carbon dioxide. In some cases 

 different pH may bring about morphological differences. For exam- 

 ple, in bacteria-free cultures of Paramecium hursaria in a tryptone 

 medium, Loefer (1938) found that at pH 7.6-8.0 the length averaged 

 86 or 87m, but at 6.0-6.3 the length was about 129^. The greatest 

 variation took place at pH 4.6 in which no growth occurred. The 

 shortest animals at the acid and alkaline extremes of growth, were 

 the widest, while the narrowest forms (about 44ju wide) were found 

 in culture at pH 5.7-7.4. Several workers have made observations 

 on the pll range of the water or medium in which certain proto- 

 zoans live, grow, and multiply, which data are collected in Table 1. 



