GROWTH 539 



The Chilomonas grew best in unaerated cultures and not so well in the 

 cultures aerated with CO2 free air. The Glaucoma grew equally well 

 with and without CO^, but better than in unaerated cultures. Jahn believes 

 that CO2 is necessary to some organisms to avert the weakening of the 

 buffer systems within the cell. The anaerobes are believed less sensitive 

 to CO2 removal because the amino acids and other weak acids may re- 

 place the carbonic acid. The lag period in bacterial growth varies with 

 the CO2 concentration (Walker, 1932), and increased production is 

 associated with physiological changes in the bacterial cells (Huntington 

 and Winslow, 1937; Gladstone et al., 1935). Similar effects should be 

 watched for in protozoan populations. 



Temperature has long been known to affect growth. Woodruff and 

 Baitsell (1911b) found that the Qj„ for the cell division of P. aurelia 

 was 2.7, over a range of 21.5° to 31.5° C, and that the optimum range 

 for them was 24° to 28.5° C. Individual pedigree cultures and mass cul- 

 tures were measured by Mitchell (1929) over a range of 12° to 27° C, 

 and the thermal increment (p) for cell division was found to be 23,000 

 calories. A lag was found in the isolation cultures, and a method is given 

 for calculating the division rates from data covering several days. Pos- 

 sibly with a different culture medium the lag might have been avoided 

 or changed. Daniel and Chalkley (1933) found [j to equal 16,500 for 

 the whole division process of Amoeba proteus (4° to 30° C). For nu- 

 clear division p equals 1 6,600 (4° to 35° C.) ; for cytoplasmic division, 

 20,500 (11° to 21° C), 7,300 (21° to 26° C); prophase 11,700, and 

 anaphase 20,200 (13° to 26° C.). The increments suggest that oxida- 

 tive processes control cell division. 



Jahn (1935) found a maximum growth rate for Euglena gracilis, 

 grown in a hydrolyzed casein medium at 10° C, but the addition of 

 sodium acetate changed the temperature of maximum growth to 23°. 

 Motility and the occurrence of encystment and palmella stages were 

 related to the temperature and food. Smith (1938) reported that Chilo- 

 monas Paramecium grew in a sodium acetate-mineral salts medium from 

 9.5° to 35° C, with an optimum range of 26° to 30.5° C. Prolonged 

 exposure to the lower temperatures decreased the resistance of the ani- 

 mals to the cold. Adaptation to changed temperature required at least 

 forty-eight hours. The synthesis of fat and starch is a result of tempera- 

 ture and in turn may control the division rate. 



The chlorophyll-containing Protozoa vary in their light requirements. 



