26 



PROTOZOOLOGY 



logical differences. For example, in bacteria-free cultures of Para- 

 mecium bursaria in a tryptone medium, Loefer (1938) found that at 

 pH 7.6-8.0 the length averaged 86 or 87/x, but at 6.0-6.3 the length 

 was about 129/z. 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 44m wide) were found in culture at pH 5.7-7.4. Many workers 

 have made observations on the pH range of the water or medium 

 in which certain protozoans live, grow, and multiply, some of which 

 data are collected in Table 1 . 



Table 1 . — Protozoa and hydrogen-ion concentration 



