74 CHEMICAL ENVIRONMENT 



of the bacteria in the Hter was about 0.001 mg. Hence the 

 bacteria used 0.002 of their weight of carbohydrate and 

 0.00007 of ammonium sulphate. A 150-pound (75-kilo) man 

 can Hve on 375 g. of sugar (0.005 of his weight) and 52.5 g. of 

 protein (0.0007 of his weight). From these figures it can 

 be calculated that the man utilizes about two and a half 

 times as much carbohydrate and about seven times as much 

 nitrogen as the bacterium, relatively speaking. 



Limitation of Growth.— Students sometimes get the impres- 

 sion from the discussion in this chapter that a bacterium is 

 immortal, it lives forever. When a bacterium divides an 

 argument might be started as to which of the two, if either, 



UNITS OF TIME 



Fig. 52.— The growth curve of bacteria. From "Life Phases in a Bac- 

 terial Culture" by R. E. Buchanan, reproduced through the courtesy of the 

 Journal of Infectious Diseases. 



is the original one. This is like the old discussion as to which 

 came first, the hen or the e^g, and need not be followed 

 further. It has been demonstrated that the life of any given 

 bacterium is relatively short. When organisms are placed 

 in a favorable environment, growth, i. e., division proceeds in 

 a very definite manner as is illustrated by Fig. 52. This is a 

 diagram illustrating growth rates and not a curve plotted 

 from one single experiment. The diagram means that at 

 first there is a period relatively short during which the organ- 

 ism remains quiet apparently does nothing, 1-a; then a period 

 of increasing growth rate, a-b; next growth at a uniform rate, 

 b-c; next decreased growth rate, c-d; then a stationary 



