GROWTH 



185 



Table 44 shows how the growth produced (= mg. 

 nitrogen fixed) by the utilization of 1 gm. of dextrose, 

 decreases rapidly with the age of the culture. The 

 amounts of the first two days are too small to be 

 determined accurately, but the efficiency measured 

 after six days is three to ten times as large as that 

 measured after the twelfth day, in all three experiments. 



The absolute efficiency can be estimated from the data of Gerlach 

 and Vogel (1902) that 1 mg. of N = 9 mg. of dry cells of Azotobader, 

 and that 1 gm. of dry cells has a combustion heat of 4.6 Cal. (Table 

 42) . This gives a utihzation of about 50 % for the first four days of 

 Experiment II, and of 30% for Exp. IV. After ten to twelve days, 

 the efficiency is only 3 to 8% (see also Linhart, p. 183). 



In well aerated cultures of Azotohacter, Hunter 

 (1923) found a constant utilization for the first eight 

 days. The mg. N fixed per gram of glucose consumed 

 were, for four successive two-day periods, 6.9, 9.37, 

 8.64, and 9.74. The average efficiency of utilization 

 of energy in this culture is much smaller than that of 

 the previous experiment. 



From Rahn's data on the lactic fermentation (see p. 400), it is 

 possible to compute the amounts of lactose required for one genera- 



Table 45. 



-Mg. Sugar Fermented during One Generation op 



Strept. lactis 



