Bacterial Multiplication 139 



sort of curve can be expected. At first the amount of food is in 

 excess of the needs of the organisms and they grow more and more 

 rapidly until they reach their peak, called the logarithmic growth 

 PHASE. As the quantity of available food becomes insufficient to 

 maintain this rate of multiplication, growth slows down at an in- 

 creasing rate. Things which cannot grow usually die, and that is 

 the fate of organisms. How long it takes a culture to become free 

 of living cells depends upon a number of factors having to do with 



"e 14.0 



.2 12.0 - 



0) 



^ 10.0 



0) 



-| 8.0 



z 



® 6.0}- 



o 



E 4.0 







^ 2.0 



1 2 



10 15 20 25 30 



Hours after Inoculation 



Fig. 26. Bacterial growth curve. (Reprinted with modifications 

 by permission of Porter, Bacterial Chemistry and Physiology, Copyright 

 1946, John Wiley and Sons, Inc., New York.) 



the environment and with the nature of the organisms; it may take 

 days, weeks, or months. 



Growth curves can be divided into four major phases: the lag 



PHASE, LOGARITHMIC GROWTH PHASE, MAXIMUM STATIONARY PHASE, 



and the phase of decline. Buchanan, however, felt that seven 

 stages could be described, each phase being distinct from the 

 others. A brief discussion of these seven steps in the growth pat- 

 tern of a typical pure culture of bacteria transferred to a fresh 

 broth medium will clarify the nature of the changes taking place 

 under such conditions. 



