70 FERMENTATION. 



regards the fermentation. But the quantity is too in- 

 significant to be considered of any practical importance. 



That the walls of the cells, which consist of cellu- 

 lose, have no effect on the fermentation, will be clearly 

 proved by the following experiments, made by me 

 nine years ago.* 



If ferment be mixed with water, and the liquid 

 filtered after standing some hours, and mixed with 

 sugar, fermentation will begin. 



If such ferment as remain on the filter be again 

 mixed with water, allowed to stand, filtered, and 

 sugar added, fermentation will be produced again in 

 this liquid. By the repetition of this experiment the 

 capability of the filtered liquid to engender fermenta- 

 tion is continually diminished, and a watery extract of 

 ferment can never decompose as much sugar as the 

 ferment itself, from which such extract is prepared. 



The ferment, after being thus washed, still retains a 

 large portion of a protein compound in the cells. For 

 if they are put in this state into a solution of sugar 

 at too low a temperature to develope fermentation, and 

 then filtered, the liquid so obtained will possess a 

 much greater power of fermentation than the simple 

 watery extract. 



By a repetition of this experiment, cells may be de- 

 prived of the greater part of their protein compound. 



At last a body remains, insoluble in water, and 

 nearly devoid of nitrogen, which, when put into sugar 



* Scheik. Onderz, deel. ii. p. 429. 



