148 



PHYSIOLOGY OF BACTERIA 



milk. No growth could occur in this very concentrated 

 cell suspension. To have a normally growing culture 

 as a check, 1 c.c. of this suspension was transferred 

 to sterile milk. Parallel experiments were made with 

 milk + 1 % peptone. 



Table 32. — Acid Formation in Milk Cultures op Strept. ghjcer- 

 inaceus by Varying Amounts op Bacteria 



Medium 



Cells per c.c. 



At start 



At end 



C.c. n/10 NaOH 

 for 10 c.c. 



At start 



After 

 120 hours 



pH 



(144 hours) 



The results of two experiments are given in Table 

 32. The milk fermented by abnormally large numbers 

 of cells shows more acid than the milk in which the 

 bacteria developed normally. This holds for titrated 

 acid as well as for pH. In peptone milk, this difference 

 in acidities is almost negligible. 



The reason is to be found in the final plate counts 

 of Experiment II. With peptone, bacteria grow to 

 much higher numbers than in plain milk. The cell 

 count of the heavily seeded peptone milk was only twice 

 as high as the final count of the peptone milk culture 

 with small seeding (3,820 against 1,640 miUions). In 

 plain milk, the difference was much larger, 7,310 against 



