56 PROTOPLASM OF PROTOZOA 



ing in hot springs at temperatures between 50° and 60° C. Motile forms 

 seem to be much more susceptible to high temperature than do en- 

 cysted forms (cysts of Colpoda are not killed at 100° C. dry heat for 

 three days), a condition probably associated with the low water con- 

 tent of the organisms (Bodine, 1923). That Protozoa show ability 

 gradually to acclimate themselves to increased temperatures has been 

 shown by Jacobs (1919). 



Since temperature changes are known to affect the rate of action of 

 molecules in liquids, it is only reasonable to assume that their effect is 

 somewhat similar upon protoplasm. In general it may be stated that a 

 slight increase of temperature over that of the normal, causes a decrease in 

 protoplasmic viscosity; a slightly higher temperature, a reversible co- 

 agulation, and a still higher temperature, an irreversible coagulation 

 and death. Davenport (1897) has referred to these conditions as con- 

 traction, heat rigor, and death rigor respectively. See also the discus- 

 sion of the action of temperature on protoplasm by Heilbrunn, 1928. 



Pantin (1924a), working on two species of marine Amoeba, found 

 that the viscosity was high near 0° C. and decreased with rise in tempera- 

 ture. The primary effect of temperature upon locomotion, he holds to be 

 a direct effect upon the change of state of the protoplasmic sol-gel trans- 

 formation. 



Perhaps one of the most complete studies of the action of temperature 

 upon protozoan protoplasm is that of Heilbrunn (1929a) on A. dubia. 

 He found that at temperatures from about 3° to 10° C, the viscosity 

 value was about 22 to 23 times that of water. From 10° to 18° C. there 

 was a very rapid decrease in viscosity, approaching about 2 to 3 times 

 that of water, while at 20° to 25° C. there was an increase in viscosity to 

 about 8 to 9 times that of water, followed by a decrease to about 2 times 

 that of water at 30° to 35° C. Although the range of Heilbrunn's experi- 

 ments was not extended beyond 35° C, he states that higher tempera- 

 tures cause a coagulation of the protoplasm. Thornton (1932) has 

 observed that the maximum viscosity of the plasmagel of A. proteus 

 occurs at 4.5° C. Between 4.5° and 30° C. the viscosity decreases pro- 

 gressively, with rise in temperature, until at 30° C. the decrease is more 

 rapid. Thornton (1935) has further found that the action of certain 

 salts does not alter the fundamental effect of temperature on the vis- 

 cosity of the plasmagel of A. proteus. Daniel and Chalkley (1932) ob- 



