106 



PHYSIOLOGY OF BACTERIA 



paper are here recalculated for the more correct Buchanan 

 formula. More recent experiments by Baker, Brew 

 and Conn (1919) are based on microscopic counts, and 

 are, therefore, to be multiplied by 1.8 if they were to 



Table 14. — Fermenting Capacity of Lactic Streptococci 

 (Mg. of acid formed per average single cell per hour) 



be compared with the others calculated from plate counts. 

 This has not been done in Table 14. 



This Table 14 shows that the average cell (by plate count) of 

 StrepL lactis produces between 10 and 15 X 10"^° mg. of lactic acid 

 per hour. This amount seems ridiculously small, but it is enormous 

 if compared with the volume of the cell. The average cell of Bad. 

 coli has been calculated to weigh about 8 X 10"^*^ mg. (see Appendix). 

 The cells of streptococci are considerably smaller and cannot weigh 

 more than 5 X 10~^° mg. 



This means then that each cell produces two to three times its own 

 weight of lactic acid per hour, or that each cell ferments two to three 

 times its own weight of lactose every hour. This is a really enormous 

 rate of fermentation, and is possible only by the enormous surface 

 of the cells (50 square feet is the surface of the bacteria in 1 liter of a 

 full grown culture, see Appendix) which allows an almost immediate 



