104 PHYSIOLOGY OF BACTERIA 



considering their mode of multiplication. The formula 

 for the '^fermenting capacity" of the average single cell 

 i.e., the amount of products formed per cell and per hour, 

 is 



^ 2.301 ' AiSqog h - log a) 

 ^ At{b - a) 



where AS is the increase in products during the time 

 interval under consideration, a the number of cells at 

 the beginning, b the number of cells at the end of this 

 interval, and A^ the time of the interval. The origin 

 of this formula is developed in Appendix p. 404. This 

 formula holds true only as long as the bacteria are 

 multiplying rapidly. When the rate of growth decreases, 

 the arithmetic average gives more nearly correct rates 

 than the above formula (see p. 407). 



(&) THE RATE OF FERMENTATION OF DIFFERENT ORGANISMS 



The rate of fermentation is not constant during the 

 entire development of a culture. The rate is fastest 

 when the culture is young; with increasing age, the rate 

 gradually decreases until it reaches zero. The causes 

 will be discussed on p. 107. The rates of fermentation 

 mentioned and compared here refer only to young, 

 actively fermenting cells. 



The rate of fermentation is of great practical impor- 

 tance in the bread yeast industry. Several different 

 methods are used for determining the fermenting 

 capacity for baking purposes. One of the old methods 

 still in use is that of Kusserow where 10 gm. of yeast, 

 40 gm. of sugar and 400 c.c. of water are mixed, and 

 where the developing CO2 forces water out of a container; 

 this water is measured; its volume corresponds to the CO2 

 volume produced. The total gas formed in two hours 



