ALCOHOLIC FERMENTATION OF SUGAR 139 



These facts have led to the very interesting series of re- 

 searches by Harden and Young. Harden showed that if an 

 equal volume of blood serum was added to the yeast juice, 

 digestion of the yeast albumin did not proceed so rapidly and 

 the activity of the zymase was increased, that is, there was a 

 more prolonged alcoholic fermentation. Harden and Young 

 further found that, besides serum, boiled yeast juice greatly 

 increased the alcoholic fermentation ; thus the total fermenta- 

 tion produced by 25 c.c. of yeast juice acting on 2'5 grams 

 of glucose, was on the average doubled by the addition of an 

 equal volume of boiled juice, and increased to a maximum when 

 three to five volumes were added, after which it decreased. 



It might be contended with equal justice either that this 

 increase of fermentation was due to an increase in the activity 

 of the zymase, to decrease in the activity of the proteolytic 

 enzyme, or to a combination of these causes. As a matter of 

 fact, the true cause is being found to lie rather deeper than 

 might at first sight be concluded. When fresh yeast juice is 

 boiled there is, as has been stated, a heavy precipitation of 

 albuminous matter ; if this is filtered off, the filtered juice 

 still increases the activity of the zymase ; this would seem to 

 indicate that the increased activity was not an enzyme effect, 

 as enzymes in general are destroyed by boiling. The unknown 

 substance is besides capable of passing through a dialyser, 

 but, on the other hand, is precipitated by 75 per cent, alcohol. 



It was possible by an ingenious experiment to show that 

 the alcoholic fermentation certainly depends on two substances, 

 neither of which is capable alone of causing fermentation. 

 By soaking an ordinary Chamberland filter candle (such as is 

 often attached to household water taps for the purpose of 

 removing organisms from the water before drinking) in melted 

 gelatine and allowing the latter to set in the pores of the filter, 

 it is possible to obtain a fairly rapid dialysis of colloidal 

 matter by filtering a solution containing such matter through 

 this gelatine filter, under high pressure. This method of 



