EXPERIMENT STATION BULLETINS. 445 



The fermentiug capacity of the single cell is really a measure of the 

 amount of enzyme in the cell. The amount of alcohol produced by one 

 cell under normal conditions indicates the amount of zymase present. 

 If two lactic cultures differ in the amount of acid formed, this may 

 be due either to a faster growirh of one of the cultures, to a greater 

 fermenting capacity, to both, or to a greater fermenting capacity 

 though slower growth. The computation of the fermenting capacity 

 decides between these various possibilities. If the fermenting capacity 

 differs, this indicates a difference in the amount of zymase per cell. 

 Since it is possible to measure the zymase in the cell, zymology might 

 use this method to advantage. At present, in order to study these endo- 

 enzymes, it is necessary to prevent the multiplication of the enzyme- 

 containing cells by chemical or physical means which usually affect the 

 enzyme also. The method suggested in this paper separates multiplica- 

 tion and fermentation by means of a mathematical formula, without 

 interfering at all Avith the natural development of the culture. 



The fermenting capacity of the single cell is in certain ways related to 

 the virulence of microorganisms which is fairly well defined in path- 

 ogenic bacteriology, but which is entirely vague if applied to dairv' and 

 soil bacteria. 



It is customary to measure the rapidity of growth of microorganisms 

 by the rate of reproduction which is the average time required b}' one 

 cell to make two cells. This time is computed from the bacterial counts 

 at the beginning and end of the experiment under the assumption that 

 bacteria multiply in geometrical progression. This is not exactly, but 

 nearly true. The rate of reproduction is not constant, of course, the 

 multiplication being much faster in the beginning and ceasing entirely 

 in old cultures. But under comparable conditions in young cultures, it 

 is possible to obtain fairly well agreeing results representing a unit 

 characteristic of the species under study. This unit may not represent 

 the actual time it takes one cell to double, in fact, we know it does not, 

 on account of our inaccurate methods of counting. It is, however, a 

 valuable working unit, and its reliability is easily tested by the devia- 

 tion in parallel experiments. 



Nothing more can be expected from the computation of the fermenting 

 capacity. It may not give the actual amount of products formed by 

 one cell, and usually it will not, the error being due mostly to the in- 

 accuracy of counting the cells and other irregularities. But it is, never- 

 theless, a working unit, the reliability of which can be proven ex- 

 perimentally. 



II. THE FORMULA FOR THE COMPUTATION OF THE FERMENTING CAPACITY. 



In this computation of the fermenting capacity it is assumed that 

 bacteria multiply in geometrical progression, and that all young cells 

 of a fresh, pure culture ferment alike. These two hypothetical condi- 

 tions are discussed in a following subtitle. 



"We shall designate the number of bacteria in the beginning of the 

 experiment as a; let i^ stand for the time in which the organisms are 

 under consideration and in which the fermenting capacity of the cells 

 is estimated, and 6 for the number of bacteria resulting from multipli- 



