GROWTH 



209 



It is an old experience that yeast is greatly favored 

 by a liberal oxygen supply. Aeration not only increases 

 the crop, but also the rate of growth, as A. J. Brown has 

 shown (1905). Hunter (1923) showed the same for 

 Azotobacter. 



Table 52. — Growth and Ammonia Formation in Peptone Solutions 

 WITH and without Sand by an Unidentified Soil Bacterium 



100 c.c. peptone 

 solution 



NHa, 

 mg. 



Plate count 



100 c.c. peptone solu- 

 tion + 1,000 gm. sand 



NHs, 

 mg. 



Plate count 



Start 



After 24 hours 

 After 48 hours 

 After 72 hours 

 After 96 hours 

 After 168 hours 







1.53 



7.48 



8.67 



12.92 



20.57 



910 

 28,200,000 

 180,000,000 

 342,000,000 

 312,000,000 

 282,000,000 



Table 53. — Growth and Acid Formation by Strept. lactis in Milk 

 WITH and without Sand 



Many of the experiments on growth rates have been made in 

 peptone solutions or meat extract solutions under the assumption 



