PROTOPLASM OF PROTOZOA 57 



served that the rate of mitosis, including nuclear and cytoplasmic divi- 

 sion, of A. proteus varies inversely with temperature from about 4° to 

 30° C. From about 30° to 40° C. these processes vary directly with the 

 temperature. 



Greeley (1904) found that the consistency of the protoplasm of vari- 

 ous Protozoa, like organic colloids, varies directly with the temperature, 

 within certain limits. As the temperature is elevated above the normal, 

 the protoplasm absorbs water, so that its fluidity and motility are greatly 

 increased. These changes continue until a critical point is reached, at 

 which coagulation occurs. The resistance of P. caudatum to a tempera- 

 ture of 40° C. has been shown to vary with the hydrogen-ion concentra- 

 tion of the medium and to exhibit two maxima of resistance: one on 

 the alkaline and one on the acid side, with a region of minimal resist- 

 ance at neutrality (Chalkley, 1930). In saline solutions the mechanism 

 of death by heat seems to vary with different hydrogen-ion concentra- 

 tions. At pW. 6 or less the cell coagulates, at pH 8 or more the organism 

 disintegrates; between these two extremes death occurs from rupture by 

 swelling. Furthermore, Chalkley also found an increase in thermal re- 

 sistance of Paramecium on the addition of Ca, and a decrease on addition 

 of K. Oliphant (1938) found that the rate at which the cilia of Para- 

 mecium beat in reverse varies directly with temperature, a condition he 

 implies is associated with changes in viscosity of the organisms. For a 

 further discussion of the effects of high temperatures on organisms, in- 

 cluding the Protozoa, see Belehradek (1935). 



It has been shown by Greeley (1901) that when Stentor coeruleus is 

 suddenly lowered to the freezing point of water, it is usually killed. 

 However, when the temperature is lowered slowly to 0° C., a remark- 

 able dedifferentiation of the animal takes place. The resorption of the 

 cilia and the gullet, and the throwing off of the ectosarc was observed, 

 and there was finally formed a spherical cyst-like undifferentiated cell, 

 which Greeley referred to as a "resting" cell. When returned to room 

 temperature, a reverse process takes place, and the cyst-like organism 

 becomes active. With the lowering of the temperature the organism was 

 observed to lose water. Greeley (1903) further found that the method 

 of reproduction in Monas could be controlled by temperature; at 20° C. 

 the organisms reproduced sexually and by fission; at from 1° to 4° C. 

 they reproduced by asexual spores. 



