130 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



growth curve to reflect this partial synchronization; however the form 

 of the curve in the period when the 5MT is added and following the addi- 

 tion of T would depend on whether actual cell division is inhibited by 

 5MT. A necessary and sufficient requirement to make the above- 

 described hypothesis agree with the experimental facts is that there 

 should be some period during which the average cell size, as measured by 



20 



40 



60 



SO 



100 



120 



140 



Fig. 2. Five methyl tryi)tophane (lO'M) was added at t = to an aliquot C 

 of a culture A of &. typhimiiriiim growing exponentially in M9 synthetic medium at 

 37°. At t = 25 min. excess tryptophane was added to an aliciuot B from C. All 

 cultures were left at 37°, and were kept between 3.5 and 7 X 10' cells/ml. by means 

 of culture dilutions for which allowance has been made in the figure. Turbidity 

 readings (solid line) and colony counts (broken line) for A were taken from t = —90 

 min to t = +200 min. and experimental points for curve A have been omitted from 

 the figure. 



Turbidity for C; turbidity for B; colony counts for C; 



colony counts for B. 



the turbidity and colony count curves, should be considerably smaller 

 than the average cell size of an exponentially growing culture. This could 

 also be expressed by the statement that there should be a period during 

 which the colony counts increase more rapidly than the turbidity, followed 

 by a period when the turbidity increases more rapidly than the colony 

 counts. Eventually, of course, the colony count curve and the turbidity 

 curve should again come together indicating that the average cell size 

 is the same as before the addition of the 5MT. Experiments of this type 

 were tried by 0. Maal0e and the author, and figure 2 illustrates the re- 



