GROV/TH 231 



will grow in nutrient broth to about one billion cells per 

 c.c. This may be a question of size or total surface: 

 Table 132 on p. 397 gives the following final numbers 

 of cells per liter: Yeast: 50,000,000; Bad. coli: 1,000,000,- 

 000; Bacteriophage: 100,000,000,000. But the weight 

 of these cells ranges in the reverse order. The total 

 crop in 1 liter of medium weighs in moist condition: 

 with aspergillus, 7,000 to 19,000 mg.; with yeast, 6,500 

 mg.; with Bad. coli, 800 mg.; with bacteriophage, 0.42 

 mg. 



The concentration of food will influence the final crop. 

 Addition of chemicals (not food) may influence the crop 

 favorably, by acting as buffer, or providing a more 

 suitable osmotic pressure, or they might decrease the 

 crop if they have a toxic action. 



(a) THE CAUSES OF THE ENDPOINT OF GROWTH 



Before the factors of concentration of food, of tempera- 

 ture and of chemical influences can be discussed, it seems 

 essential to try to come to a clearer understanding of the 

 cause of cessation of growth. This question has already 

 been raised regarding the decrease of the growth rate 

 (p. 199). It was not answered in a satisfactory way. 

 Many conflicting experimental data have to be analyzed, 

 and many conflicting theories must be considered. 



It should be realized from the beginning that different 

 organisms may cease to grow from different reasons, and 

 that the growth of the same organism in different media 

 may stop from different reasons. Theories on the limit- 

 ing factor of Streptococci cannot be disproved by experi- 

 ments with Bad. coli or with yeasts. 



It must be further kept in mind that the rate of growth 

 is independent of the flnal amount of growth. While 

 the rate was found to be but slightly influenced by the 



