THEORY OF FERMENTATION 301 



cooled by artificial means; the end of the escape tube was 

 then taken out of the still boiling dish and plunged into the 

 mercury trough. In impregnating the liquid, instead of em- 

 ploying the contents of the small cylindrical funnel whilst 

 still in a state of fermentation, we waited until this was 

 finished. Under these conditions, fermentation was still 

 going on in our flask, after a lapse of three months. We 

 stopped it and found that 0.255 gramme (3.9 grains) of 

 yeast had been formed, and that 45 grammes (693 grains) 

 of sugar had fermented, the ratio between the weights of 

 yeast and sugar being thus -Jk| |-*- = T ^- Tt In this experiment 

 the yeast developed with much difficulty, by reason of the 

 conditions to which it had been subjected. In appearance 

 the cells varied much, some were to be found large, elon- 

 gated, and of tubular aspect, some seemed very old and 

 were extremely granular, whilst others were more trans- 

 parent. All of them might be considered abnormal cells. 



In such experiments we encounter another difficulty. If 

 the yeast sown in the non-aerated fermentable liquid is in 

 the least degree impure, especially if we use sweetened 

 yeast-water, we may be sure that alcoholic fermentation will 

 soon cease, if, indeed, it ever commences, and that accessory 

 fermentations will go on. The vibrios of butyric fermenta- 

 tion, for instance, will propagate with remarkable facility 

 under these circumstances. Clearly then, the purity of the 

 yeast at the moment of impregnation, and the purity of the 

 liquid in the funnel, are conditions indispensable to success. 



To secure the latter of these conditions, we close the 

 funnel, as shown in FIG. 2, by means of a cork pierced with 

 two holes, through one of which a short tube passes, to 

 which a short length of india-rubber tubing provided with 

 a glass stopper is attached; through the other hole a thin 

 curved tube is passed. Thus fitted, the funnel can answer the 

 same purposes as our double-necked flasks. A few cubic centi- 

 metres of sweetened yeast-water are put in it and boiled, 

 so that the steam may destroy any germs adhering to the 

 sides; and when cold the liquid is impregnated by means of 

 a trace of pure yeast, introduced through the glass-stoppered 

 tube. If these precautions are neglected, it is scarcely pos- 

 sible to secure a successful fermentation in our flasks, be- 



