EXPERIMENT STATION BULLETINS. 



459 



V. THE INFLUENCE OF AGE. 



lu the introduction, it lias been stated that the fermenting capacity 

 is not a constant quality of the cell, but it changes like the rate of 

 multiplication, and though it probably varies but little in the early 

 stage of growth, it decreases rapidly as the fermentation products ac- 

 cumulate. In order to obtain comparable results, it is therefore nec- 

 essary to use young cultures. The comparison would be absolutely 

 correct only, if all experiments were carried on until an arbitrai*y 

 standard concentration of fermentation products has been reached. This 

 is not always possible, however, since too much work is required in 

 Avatching the cultures so closely. 



Variation of the Fermenting Capacity during the Entire Develop- 

 ment of a Culture. The formation of acid in cultures of Bacterium 

 lactis acidi is soon checked by an accumulation of products which in- 

 terfere with further fermentation. The retardation of the acid forma- 

 tion naturally causes a decrease of the fermenting capacity. This is 

 l)lainly demonstrated in the following experiment where acidity and 

 bacterial numbers of a pure culture of Strain II were determined every 

 tliree hour's for 36 hours. The two series dift'er only in the amount of 

 culture A having 1,000 times as many cells at the start as 

 For G and 12 hours respectively no increase in acidity is 

 The first increase is very small and cannot be determined 

 accurately; hence the deviation in the fermenting capacity. After that, 

 the fermenting capacity is fairly constant until an acidity of .50-60° 

 has been reached. From then on, the' decrease is very rapid. Multipli- 

 calion ceases earlier than fermentation. (See table on next page.) 



This experiment Avas carried |0n for the purpose of demonstrating 

 that there is no evidence of an early stage of growth without fermenta- 

 tion. From the time the first traces of acid can be determined, the data 

 show that the younger the culture, the faster is the fermentation caused 

 by each single cell. What happened before the acid could be deter- 

 mined, we have no means of telling. It can be easily calculated, how- 

 ever, tliat if the cells formed acid during this period at the normal 

 rate, the amount Avould be Avithin the limits of analj-tical error. 



Similar results are found in several of the later experiments, and 

 there is not a single exception to this rule. A feAV of the data are com- 

 piled in the following table: 



inoculation, 

 culture B. 

 noticeable. 



