EXPERIMENT STATION BULLETINS. 443 



THE FERMENTING CAPACITY OF THE AVERAGE SINGLE CELL 



OF BACTERIUM LACTIS ACIDI. 



Teclinical Bulletin No. 0. 



BY OTTO RAHN. 



Page 



I. Introduction 447 



II. The Formula for the Coniiputation of the Fermenting 



Capacity 445 



III. Discussion of the Assumptions in the Previous Chapter. . . . 448 



IV. Fenuenting Capacit}' of various Strains 454 



V. Influence of Age 459 



VI. Influence of Food 470 



VII. Influence of Temperature 478 



VIII. Conclusions 480 



INTRODUCTION. 



Under ''fermenting capacity of the average single cell" is understood 

 the amount of products formed by an average cell of a certain species 

 of microorganisms in one hour. This factor can be estimated in cer- 

 tain cases with a fair degree of accuracy, and it is the object of this 

 paper to show how this can be done and how it is a valuable, perhaps 

 even a necessary factor for the understanding of certain problems of 

 fermentation. It will naturally be of no value to the manufacturer of 

 fermentation products who consider microorganisms simply as the cheap- 

 est means of obtaining the desired products. But it may contribute to the 

 understanding of fermentation processes, since it enables us to estimate 

 the fermenting power of the individual cell, independent of its multi- 

 ])lication. The desire of microbiologists to know how much of a certain 

 product is formed by one cell in a certain time is not unreasonable. 

 Rubner,* in his studies conceiiiing the energy retiuirements of bacteria, 

 says : "It would seem to us inconceivable that anybody Avould study 

 the consumption of foods or the formation of metabolic products by 

 two species of animals without ascertaining how many individuals of 

 each species are present and how much body weight they represent. If, 

 therefore, metabolic experiments are supposed to have any real value, 

 they must be connected with some kind of determination of the final 

 crop of microorganisms." 



If bacteriologists do not record the amount of living matter enter- 

 ing into reaction, it is simply because this seems impossible, on account 

 of the minuteness of organisms and because of the continuous change 



*Arch;v f. Hygiene Bd. 48 (1904) p. 2S4. 



