58 PROTOPLASM OF PROTOZOA 



According to Luyet and Gehenio (1938), Becquerel (1936) found 

 that certain Amoeba in dry soil were not killed when subjected to 

 — 269° to — 271° C. for 7.5 days, or when subjected to ^190° C. for 

 480 hours. See the above-mentioned work of Heilbrunn (1929a) for 

 absolute viscosity values of the protoplasm of A. duhia at low tempera- 

 ture. 



Chambers and Hale (1932) observed that Amoeba exposed to — 5° 

 C. were not killed. However, by inserting an ice- tipped pipette into the 

 interior of the organism, fine feathery crystals of ice were observed to 

 appear immediately at — 0.6° C. 



In general it may be stated that low temperatures tend to increase the 

 viscosity and thus to decrease the rate of locomotion, and to favor cyst 

 formation in Protozoa. Motile forms are usually killed as the tempera- 

 ture of the water reaches 0° C. However, the Protozoa show some degree 

 of acclimatization to low temperatures. 



MECHANICAL AGITATION 



Mechanical agitation may cause a marked change in the consistency 

 of Amoeba protoplasm, apparently by causing a breakdown (thixotropic 

 collapse) of its internal structure. Chambers (1921) has shown that 

 churning Amoeba by microneedles caused a liquefaction of its proto- 

 plasm. Vigorous shaking (Angerer, 1936) caused at first a liquefaction 

 of the plasmasol of A. dub'ia, followed by an increase in viscosity; con- 

 tinued agitation caused the complete dissolution of the organism. How- 

 ever, in A. pro tens agitation caused a decrease in viscosity in the plasma- 

 gel to a minimum, without the subsequent increase observed in the 

 plasmasol of A. dub'ia. High-frequency sound waves have been observed 

 to produce whirling of the inclusions in the small vacuoles of A. proteus 

 and A. dubia; higher intensities cause a mild whirling of the more liquid 

 regions, followed by rupture of the organisms (E. N. Harvey, E. B. 

 Harvey, and Loomis, 1928). A decrease in viscosity of the endoplasm 

 was also observed. 



HYDROGEN-ION CONCENTRATION 



That Protozoa can live in wide ranges of hydrogen-ion concentrations 

 is evident from the work of Alexander (1931) on Euglena which he 



