AGE Or CULTURE 



ACE OF SUBCULTURE 



AGE OF CULTURE 



Fig. 162. Growth curves of microorganisms in a limited volume of culture 

 medium. Note that the logarithm of the total number of cells at any one time 

 has been plotted against the age of the culture. In this sort of plot a straight 

 line means that each microorganism is growing and dividing at a constant rate. 

 Another way of expressing this phase of growth is to say that the number of 

 cells doubles at regular time intervals. Upper left: A few microorganisms are 

 put into a fresh culture flask. They may show a short latent period but soon a 

 plot of the logarithm of the cell number against time gives a straight line. After 

 this period of constant growth (logarithmic growth) the cell divisions fall off 

 rapidly and a steady state is attained where the number of individuals in the 

 culture does not increase. Upper right: Some of the animals from the culture in 

 the stationary state are placed in a fresh culture medium (subculture). These 

 animals do not begin to divide immediately but show a short latent period. They 

 then exhibit the same kind of growth as was originally obtained. Bottom: The 

 logarithmic phase of growth can be extended by increasing the concentration of 

 the food in the medium, C x , C 2 , C 3 , and C 4 . There is a limit, however, to the 

 effect of increased concentration of food. 



